Consanguineous marriage has been the culturally preferred form of marriage in Iran. This paper examines the extent to which education, urbanization and changes in modes of economic production have affected the incidence of consanguineous marriage and attitudes towards consanguineous marriages. The 2002 Iran Fertility Transition Survey conducted in the four provinces of Gilan, Sistan and Baluchistan, Yazd and West Azarbaijan provides information on the degree of relationship of marriage partners from around 6550 ever-married women aged 15–49. Attitudinal data were also obtained. Overall, the level of marriage to biological relatives ranged from 23% in Gilan to 78% in Sistan and Baluchistan. The paper finds that the practice of marriage to biological relatives has remained surprisingly resilient in the face of modernizing influences and that ethnicity, province and area of residence remain important determinants. On the other hand, attitudes have shifted towards marriage with a non-relative. Anthropological research would illuminate the processes of consanguineous marriage in Iran.