Turkey has high levels of infant mortality and consanguineous marriages. It has had a high level of infant mortality for its economic level for many years. Over recent decades, although adult mortality rates have not been very different from those of other countries with similar socioeconomic structures, its life expectancy at birth has remained low due to its high infant mortality rate. This has been called the Turkish Puzzle. According to the Turkey Family Structure and Population Issues Survey, 27% of women had a consanguineous marriage in 1968. Subsequent Turkish Demographic and Health Surveys (TDHSs) found the rate of consanguineous marriages to be stagnated at 22–24%, with a resistance to reduction. According to the TDHS-2008, 24% of women had a consanguineous marriage. Numerous studies in various countries of the world have indicated that consanguineous marriages, particularly of first-degree, have the effect of increasing infant mortality. The main aim of this study was to assess the causal impact of consanguineous, particularly first-degree consanguineous, marriages on infant mortality, controlling for individual, cultural, bio-demographic and environmental factors. Data were merged from four Turkish DHS data sets (1993, 1998, 2003 and 2008). Multivariate analysis revealed that first-degree consanguineous marriages have increased infant mortality by 45% in Turkey: 57% in urban areas and 39% in rural areas. The results indicate that there is a causal relationship between consanguineous marriages and infant mortality. This finding should be taken into account when planning policies to reduce infant mortality in Turkey, and in other countries with high rates of consanguineous marriage and infant mortality.