Is It Legal To Marry Your First Cousin?

Is It Legal To Marry Your First Cousin?

Throughout history, people from different cultures took the idiom “keeping it in the family” to the extreme by marrying their own relatives. In one of the more famous examples, Cleopatra of Egypt married both of her brothers so they could jointly rule the land. While the practice of marrying your siblings is now archaic (not to mention extremely icky), is it legal to wed a close relative such as a first cousin?

Young married couple image from Shutterstock

When I was a young girl living in Hong Kong, my parents told me that I was allowed to marry my first cousin so long as they don’t share the same surname. Just to make it clear, they were by no means encouraging it, and considering my mum’s side of the family were prone to having daughters, I didn’t really have many options in terms of eligible cousins. But legally, my parents are correct: in Hong Kong, you can marry a first cousin who has a different surname.

In Australia, it’s even more straightforward: legally, you can marry your first cousin, plain and simple. According to section 23B of the Marriage Act 1961:

(2) Marriages of parties within a prohibited relations are marriages: (a) between a person and an ancestor or descendant of the person; or (b) between a brother and sister (whether of the whole blood or the half-blood).

You’re also not allowed to marry a child you have adopted (would you want to be another Woody Allen anyway?). But under Australian law, you are allowed to marry a cousin, niece or nephew and even an aunt or uncle.

According to

In some countries it is illegal to marry your first cousin, but not Australia. Some communities in Australia have a much higher rate of first cousins marrying than others, believing there are cultural, extended family, social, religious and financial benefits in the practice.

Now you might be under the impression that marriage to a first cousin may be akin to gene pool genocide given that any child produced from the union would be prone to birth defects. If you’ve done biology in high school, your teacher may have explained to you that you need variety in the DNA make up of a child to reduce the chances of hereditary diseases. Because if you and your cousin both have a defective gene, your kid will most likely get it.

But a large-scale study done by UK researchers in 2013 showed that while babies born to couples that are related increases the rate of babies born with health problems, the chances are smaller than people would think. The risk of defects is about the same as women having babies when they’re over 34, according to the study.

Regardless of whether you agree with the morality and science behind marrying a first cousin, we’re only interested in the legal aspects of the issue here. So long as you’re not forced into a marriage with a relative, if you really do want to marry your cute cousin, that’s your legal and personal prerogative.

Did you just catch yourself wondering if something was legal or not? Let us know and we may be able to answer it in our next Is It Legal? feature.


  • The measure of how genetically close the average marriage is is ‘consanguinity’.

    There are some amazing maps of consanguinity available.
    Try overlaying a consanguinity map with a map of majority-Muslim countries.

    The Arabs had worked out that cousin-marriage was a bad idea, but Muhammad changed this by marrying his first cousin. Islam allows and encourages cousin-marriage.

  • Isn’t it that the more you marry first cousins, the worse the genetic defects get, so if it’s only once in a while it’s not that big a deal, if it’s consistently then you get the european royal families…

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