Objectives: The aim of the study was to determine the extent and nature of consanguinity in the Qatari population and its effects on common adult diseases. Subjects and Methods: The study was conducted in urban and semi-urban areas of Qatar between October 2004 and May 2005. The total sample of 1,050 married Qatari females 15 years of age and over were approached for study. The degree of consanguinity between each female and her spouse and the degree of consanguinity between their parents were recorded. Results: Of 1,050 married Qatari females who were approached, 876 agreed to participate in the study, giving an 83.4% response. The rate of consanguinity in the present generation was 51% (95% confidence interval = 47.7-54.4) with a coefficient of inbreeding of 0.023724. The consanguinity rate and coefficient of inbreeding in the current generation were significantly higher than the maternal rate (51.0 vs. 40.3%; p < 0.001; 0.023724 vs. 0.016410 maternal). All types of consanguineous marriages were higher in this generation, particularly first cousins (26.7 vs. 21.4% paternal and 23.1% maternal) and double first cousins (4.3 vs. 2.9% paternal and 0.8% maternal). The current generation of consanguineous parents had a slightly higher risk for most diseases: cancer, mental disorders, heart diseases, gastro-intestinal disorders, hypertension, hearing deficit and diabetes mellitus. All reported diseases were more frequent in consanguineous marriages. Conclusion: The study showed that in a population with a high rate of consanguinity, there is a significant increase in the prevalence of common adult diseases like cancer, mental disorders, heart diseases, gastro-intestinal disorders, hypertension and hearing deficit. Copyright (C) 2007 S. Karger AG, Basel.