Since 1 August 2025, Austrian law no longer permits a marriage between relatives up to and including the fourth degree of the collateral line. If a biological relationship is discovered after the wedding, the first questions are the legal degree of relationship and the date of the marriage.
For first cousins, the line through the shared grandparents generally leads to the fourth degree of the collateral line. Section 25 of the Austrian Marriage Act provides that a marriage is null if it was concluded between blood relatives in breach of the prohibition in section 6.
This article focuses on the relationship prohibition and possible nullity. Annulment for duress or mistake, affinity, adoption and general divorce consequences are separate legal questions.
What should be clarified first after a relationship is discovered?
This short check separates the wedding date, the family line and foreign-law issues.
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Which situation best describes your case?
Choose the point closest to your situation. The orientation does not replace a review of the documents and procedure.
Overview of all answers.
Review the relationship degree and possible nullity under the current Act
Map the family line using birth records and a family tree. For first cousins, check whether the documented ancestry actually leads to the fourth degree of the collateral line and whether section 25 applies.
Review temporal applicability without assuming retroactivity
For a marriage entered into before 1 August 2025, the current version of section 6 cannot simply be applied retroactively. The law in force at the time, the place of marriage and the complete documents must be reviewed.
Clarify the foreign element and the ancestry evidence separately
For a marriage entered into abroad or unclear ancestry, the current Austrian section 6 does not provide an automatic answer. Clarify the place of marriage, the nationalities, the relevant records and recognition in Austria.
Which relationships section 6 covers from 1 August 2025
Section 6 of the Austrian Marriage Act names two groups: relatives in the direct line and relatives up to and including the fourth degree of the collateral line. People are in the direct line when one descends from the other. The collateral line concerns relatives who descend from a shared ancestor without descending directly from one another.
The word cousin is therefore not enough by itself. The review must identify the shared ancestor and count the births connecting the two people through the family line. For first cousins, the documented route through the shared grandparents generally reaches the fourth collateral degree.
The provision concerns the prohibition on entering into a marriage. It does not answer every question about a marriage already entered into, a marriage before 1 August 2025 or a marriage entered into abroad. Those issues require a separate temporal and conflict-of-laws review.
How the fourth degree is calculated for first cousins
The degree calculation becomes clear when the shared ancestor is shown in the family line. From the first person, the line runs to a parent and then to the shared grandparent. It then runs through the other parent to the second person. The four births in that route form the fourth collateral degree.
This calculation assumes that the shared ancestry has been established. A family story, a similar surname or an oral statement may justify an inquiry, but it does not replace civil-status records. If several possible lines exist, each line should be documented separately.
More distant relationships may fall outside the prohibition, while a direct-line relationship is covered independently of the collateral degree. The legal classification should therefore not be derived from the everyday word relationship alone.
What section 25 means for nullity
Section 25 provides that a marriage is null if it was concluded between blood relatives in breach of the prohibition in section 6. The review therefore has two connected parts: whether a documented biological relationship covered by section 6 exists and whether the marriage was entered into despite that prohibition.
Nullity is distinct from divorce and from annulment based on a defect in consent. Divorce concerns the dissolution of a valid marriage. Annulment concerns specific defects in the formation of the marriage. The issue discussed here is the statutory prohibition based on the relationship between the spouses.
Section 25 does not provide a general answer for every family connection. Affinity is not biological blood relationship. The labels in-laws or adopted persons also do not replace a concrete review of the statutory relationship and the applicable law.
The date is part of the review: The RIS version of section 6 shows an effective date of 1 August 2025. An older marriage cannot be treated as null solely by applying today's wording. For a foreign marriage, recognition under the applicable law must also be assessed.
Which dates and records matter for the review
The review starts with the exact date and place of the marriage. The biological ancestry of both spouses is then traced through the relevant parents and grandparents. Only with these points can it be assessed whether the current section 6 applies in time and substance.
The initial file should contain the marriage certificate, birth records, records of name changes and available proof concerning the shared ancestors. For foreign records, origin, completeness, translation and any certification must be considered separately.
If the records conflict, the uncertainty should be recorded openly. The legal assessment should not rest on an assumed family history. The decisive question is what ancestry can be established from the available evidence.
Four review steps keep the questions separate
Each step answers a different question in the nullity review.
| Review step | Specific question | Significance |
|---|---|---|
| Marriage | When and where was the marriage entered into? | Set the applicable temporal and territorial framework |
| Ancestry | Which shared ancestors are shown by the records? | Determine biological relationship and degree |
| Prohibition | Is there a direct line or collateral line up to the fourth degree? | Classify section 6 as the relevant prohibition |
| Legal consequence | Does section 25 apply in the specific case? | Separate nullity from divorce and annulment |
An older or foreign marriage raises additional temporal and conflict-of-laws questions.
A useful order for tracing the family line
A structured record prevents the relationship degree and legal consequence from being conflated.
Date the marriage
Record the marriage certificate, place and date in full.
Map the family line
Enter both lines up to the shared ancestor in a family tree.
Classify the degree
Count the births in the collateral line and distinguish it from the direct line.
Review the consequence
Assess sections 6 and 25 and, where relevant, recognition questions together.
What remains open for an older or foreign marriage
If the marriage was entered into before 1 August 2025, the effective date of today's section 6 does not establish retroactive application. The law in force at the time of the marriage and any relevant transitional rules must be reviewed.
For a marriage entered into abroad, the Austrian text likewise does not provide an automatic answer. The place of marriage, the nationalities, the applicable law and the requirements for recognition in Austria must be clarified.
These points are separate from the ancestry question. Even if a shared ancestor is established, an older or foreign marriage does not receive an automatic answer about current civil status. The records and the correct procedural route must be reviewed together.
Which documents are useful for the initial review
Prepare the marriage certificate, the birth records of both spouses and the records of the parents and shared ancestors. Add a simple family table with names, dates of birth, places and the documents supporting each entry.
Where names differ, marriage, divorce or name-change records help identify each person. Foreign records should be supplied with all available translations and certifications so their use can be assessed separately.
Also record when the relationship was discovered and which information has already been provided. This makes the later review traceable without treating an initial inquiry as proof of nullity.
Frequently asked questions about marriage and relationship prohibitions
Have marriages between cousins been prohibited in Austria since August 2025?
In the version shown in the RIS, section 6 prohibits marriages between relatives up to and including the fourth degree of the collateral line with effect from 1 August 2025. For first cousins, the concrete classification of that collateral line must be checked.
Why does the relationship between first cousins count as the fourth degree?
The line runs from the first person through a parent to the shared grandparent and from there through the other parent to the second person. These four births form the collateral degree. The records must establish that the shared ancestor is in fact the same.
Does this mean the marriage is automatically a divorce?
No. Section 25 links nullity to a marriage between blood relatives in breach of section 6. That is distinct from divorce based on the breakdown of the marriage and from annulment for duress or mistake.
Does the prohibition apply to a marriage entered into before 1 August 2025?
The current section 6 cannot be applied retroactively without a separate review. The marriage date, the law in force at that time and the procedural route are relevant.
What if the marriage was entered into abroad?
A foreign marriage cannot be assessed automatically under section 6 alone. The place of marriage, nationalities, applicable law and recognition in Austria must be reviewed from the records.
Which documents should I collect?
Keep the marriage certificate, birth records, records for the shared ancestors, name-change records and, for a foreign marriage, translations and certifications. A dated family tree makes the degree review easier.
Further preparation resources
Marriage contract and notarial deed in divorce
Review asset rules and formal agreements before taking the next legal step.
Preparing an amicable divorce
Record open questions and documents before a joint application.
Amicable divorce
Overview of requirements and points for an agreement.
Documents for divorce
Collect the key documents for an initial legal review.