The union of individuals with a common ancestor may lead to serious health consequences in their offspring. Consanguinity is high in Middle Eastern communities; it was around 26% in 1988. The objective of this study was to determine the prevalence of consanguinity in Beirut and other Lebanese regions, and its associated factors in different subgroups. The cross-sectional study was performed on a convenience sample of married women in Lebanon. The women were administered a standardized questionnaire in a face-to-face interview by independent enquirers. Among 1556 women, the overall prevalence of consanguineous marriages was 35.5%, and the consanguinity coefficient was 0.020; 968 marriages (62.2%) were not consanguineous, 492 (31.6%) were first cousin, 61 (3.9%) were second cousin and 36 (2.3%) had lower degrees of consanguinity. Beirut suburb dwelling, low education subgroups, women working in the home and non-Christian religion presented the highest rates of consanguinity (p<0.05). Consanguinity is associated with couples' nulliparity and child chronic morbidity. Factors that could affect consanguinity are having consanguineous parents, having a favourable opinion towards consanguinity, choosing a spouse for religious reasons, particularly in Islam, woman having a low education, woman working in the home and women thinking that consanguinity would not lead to serious diseases. Consanguinity is therefore still a prevailing problem in Lebanon. Specific health education, and genetic counselling in particular, are suggested to explain the consequences of consanguinity to the general population and to help couples make informed choices.