Dor Yeshorim, a genetic testing programme focusing on the ‘genetic compatibility’ of prospective couples in Orthodox Jewish communities in Europe, the US and Israel, is at the centre of our paper. We discuss the specific understandings of risks that enable the effective implementation of the Dor Yeshorim model in Orthodox populations. Furthermore, we compare Dor Yeshorim to the premarital genetic testing programme for thalassaemia in Cyprus and analyse the particular social practices which generate different notions of genetic identity in these two projects. In the Cypriot programme, where individual carrier status is disclosed, unfavourable genetic carrier status is conceptualized on the individual level and often solved by resorting to prenatal genetic diagnosis upon pregnancy. In the case of Dor Yeshorim, where no information on carrier status but only on the ‘genetic compatibility’ of both partners is revealed, a notion of ‘genetic couplehood’ arises which conceptualizes ‘genetic risk’ not individually but as a matter of genetic jointness. If a prospective couple is found out to be ‘genetically incompatible’, marriage plans usually are cancelled. Furthermore, by not disclosing individual carrier information, Dor Yeshorim successfully avoids a pressing issue which ‘secular’ genetic testing programmes struggle with: the peril of ‘knowing too much’.