The aim of this study was to determine the prevalence and sociodemographic correlates of consanguineous marriages in Turkey using data derived from the 2003 Turkey Demographic and Health Survey (TDHS-2003). Demographic surveys conducted in the last 40 years consistently show that Turkey is a country with a high level of consanguinity. In the latest demographic survey (TDHS-2003), a nationally representative sample of 8075 ever-married women, consanguineous marriages accounted for 22% of the total, which is equivalent to a mean coefficient of inbreeding (α) of 0·011. There are changing secular profiles in the rates of consanguinity in general and of the specific sub-types of cousin marriages in particular in Turkey. The prevalence of first cousin marriages among all consanguineous marriages presents a steady decline from one marriage cohort to the next. The changes observed over time may be attributable to several factors such as the increase in educational level of women, the nuclearization of the family system, the mobility from rural to urban settings, a better socioeconomic status of families, an increase in women’s labour force participation in formal sectors, lower fertility rates resulting in a smaller number of cousins available for marriage, and an increased awareness of the effects of consanguineous unions on child health in cases where there is an inherited recessive disease in the family. Any attempts to discourage consanguinity at the population level appear to be inappropriate and undesirable, especially when the consanguineous union remains an integral part of the cultural and social life of Turkey. Nevertheless the WHO-recommended approach to minimizing the negative effects of consanguinity on child health should be followed, i.e. the identification of families with a high risk of a genetic disease and the provision of prospective genetic counselling.