A total of 8641 married couples were investigated from 28 Iranian populations for consanguineous marriages and coefficient of inbreeding. The results showed considerable differences in the rate and kind of consanguineous matings among the various urban, rural, tribal, and religious populations studied. The observed frequencies of the consanguineous matings in the populations of Iran are higher than those reported previously for the Middle Eastern populations. First cousin matings occurred more than second cousin matings among most of the groups studied. Uncle-niece matings occurred only among the Jews. The observed results were expected, considering the cultural, ethnic, and religious differences, and also the ecological and geographical conditions of the populations studied.