And for British Pakistanis the practise is common with an estimated 55 percent of them doing so.
For some Muslim girls it is an arrangement they agree to in order to keep their families happy, as Bradford-born Hiba Maroof discovered in BBC Three documentary 'Should I Marry My Cousin'.
The 18-year-old is faced with the dilemma of whether she should follow family tradition and marry a cousin or tie the knot with a man of her own choice.
Hiba speaks to family members and also other British Pakistani women who are at the same crossroads as her.
Her 18-year-old cousin Amin sums up the pressure they face when she tells her: 'Sometimes you have to listen to your parents as well to keep them happy. So if you don’t listen to your parents they think that you don’t love them.'
Hiba admits she has concerns over the health issues of interbreeding.
A recent report revealed that while British Pakistanis were responsible for three per cent of all births, they accounted for 30 per cent of British children born with a genetic illness.
'That many children shouldn’t be disabled if it can be helped.
'I’m not going to lie the genetic talk scares me,' Hiba said.