Genealogy, marriage structure, inbreeding and its effects in Taimyr Nganasans have been studied in detail. The population size in 715. 223 pairs were analysed. Uncle-niece and first cousin marriages were absent. Marriage frequency of second cousins and more remote relatives is 20.0%. Average inbreeding coefficient of the population is 0.0022 with some variation among three subpopulations (0.0015-0.0027). Consanguineous marriages are characterized by lower average number of livebirths, living children, stillbirths and miscarriages. There are some difficulties in the interpretation of the differences received because of a higher incidence of repeated marriages between relatives; 6 cases of hereditary diseases were registered among the offsprings of nonconsanguineous marriages, including two cases with one parent inbred.