This study examines the frequency of consanguineous marriage and coefficient of inbreeding in the State of Qatar. The study was conducted in semi-urban areas of Doha between January and May 2004. A sample of 1515 married Qatari females aged 15 years and over participated. The degree of consanguinity between each female and her spouse, and degree of consanguinity between their parents were recorded. The rate of consanguinity in the present generation was high (54·0%) with a coefficient of inbreeding of 0·02706. The commonest type of consanguineous marriage was between first cousins (34·8%). Double first cousin marriages were common (3·1%) compared with other populations. The consanguinity rate in the State of Qatar has increased from 41·8% to 54·5% in one generation.