This paper addresses attitudes towards premarital sex among second-generation descendants of Turkish migrants and their non-migrant counterparts in six western European countries. Attitudes towards virginity at marriage are crucial for understanding changes within populations or demographic variation between social groups. On one hand, the liberalization of so-called family values is seen as an important driving force of the Second Demographic Transition in western Europe. On the other hand, western European countries have become increasingly heterogeneous due to large-scale immigration. Research on union and family formation has shown persistent differences in the patterns between immigrant and native groups, in particular a strong interrelation between the life-course events leaving the parental home, union formation and marriage as well as childbearing among immigrants from countries with a Muslim tradition. Therefore, it is important to study cultural assimilation among immigrants. Yet, attitudes towards sex and marriage have become only recently a topic in studies on immigrants in western Europe. We used data of the project on The Integration of the European Second Generation (TIES 2007-08) from Austria, France, Germany, The Netherlands, Sweden, and Switzerland. The sample consisted of 4770 respondents (aged 18 to 35 years) of which were 49.5% Turkish migrant descendants. The respondents were asked whether sexual relations before marriage were acceptable for men and for women. The possible answers were “never”, “in specific cases”, and “always”, which we use as the dependent variable in a multinomial regression analyses. We investigate three research hypotheses: 1) Taking assimilation theory as our point of departure, we assume that second-generation Turks may hold more conservative attitudes than natives. 2) We test the comparative integration theory assuming to find cross-country variation in attitudes towards virginity. 3) We explore the determinants of the attitudes towards premarital sex, in particular gender, education, and religiosity.