The aim of the study was to estimate the prevalence and sociodemographic predictors of consanguineous unions in the State of Qatar and to assess the association between consanguinity, fertility and child health. A representative sample of 1800 Qatari women aged >= 15 years was approached for the study. Of these, 1515 (84.2%) women agreed to participate. The consanguineous marriage rate was 54.0% with estimated population confidence limits of 52.3-55.7%. First cousin unions were the most common form of cousin marriage. The level of parental consanguinity (both in the respondent's parents and her parents-in-law) was quite high. In a multivariable analysis, both education of the respondent and her husband as well as parental consanguinity were found to be strong predictors of consanguineous unions in the index generation. Although fertility was high in both groups, the mean number of pregnancies was somewhat higher in respondents with first cousin unions. Concomitantly they also had a slighter higher rate of livebirths than women in non-consanguineous unions. The occurrence of asthma, mental retardation, epilepsy and diabetes was significantly more common in offspring of all consanguineous than non-consanguineous couples.