Egyptian Nubians, who lived in an isolated area for many centuries, have migrated because of the construction of the Aswan High Dam and the subsequent flooding of their lands. They have settled in the valley of Kom Ombo, north of Aswan. Three major groups of Nubians can be distinguished: Fadetchi, Kenuzi and Arabs. Each group has its characteristic language and traditions, and constitutes an almost closed community. This report, one of a series on the genetical characteristics of the Nubian population, deals with the types and frequency of consanguineous marriages. A large number of married people and well-grown schoolchildren were interviewed. Analysis of the data showed that the Nubians have remarkably high consanguinity rates. These were 72.9, 75.4, 80.4% for the Fadetchi, Kenuzi and Arab communities. Amongst the consanguineous marriages, those of first cousins accounted for 45.5, 47.2 and 41.5% of the totals for the Fadetchi, Kenuzi and Arabs, respectively. The distribution of the different types of marriages, both of first cousins and of remote relations, was not random and seemed to be subject to effective social factors. The bearing of these very high frequencies of consanguineous marriages on the fertility, morbidity and mortality of Egyptian Nubians is emphasised.