The frequency of consanguineous marriage in Eastern Turkey: Objective: The rate of consanguineous marriage (CM) varies depended on different factors such as race, characteristics of population, and religion and moral features in different countries. Gene frequency and genetic structure are changed by CMs. The aim of the present study is to assess the prevalence of CM and its effects on miscarriage, stillbirth, congenital malformation and ratio of newborn death. Methods: This study was performed in Van region, Eastern Turkey, between September 2005 and April 2006. A total of 650 families from 24 districts chosen in accordance with the number of inhabitants were included in this study. First cousin marriages were accepted as a first degree CMs, sesquialter and second cousin marriages as second degree and marriages between distant relatives were accepted as a third degree CM. Monthly income of the families was classified in accordance with minimum wage determined by government. Results: Of all families, 224 (34.4%) had CM, and 168 (75%) had first-degree consanguinity. A lower CM rate was found in mothers who graduated from secondary school or upgrading (p <0.01). However, no relationship was found between CM and fathers' education level. While a low CM rate was found in families who had two or less children (p <0.01), high rate was observed in families who had five or more children. In addition, a high rate of miscarriage, stillbirth and mental-motor retardation was found in families with CM (p <0.05). The rate of child mortality between the aged 0-2 years was found to be higher in families with CM (p <0.01). The higher CM rate was observed in families who married due to pressure or insistence of their families than married voluntarily (p <0.05). Conclusion: Our study showed that CM rate was very high, 34.4%, in our region Eastern Turkey.