Two studies were undertaken. Firstly, congenital heart defect (CHD) data from the Saudi Arabian Congenital Heart Defects registry (CHD registry) were compared to data published by the Baltimore-Washington Infant Survey (BWIS) group and the European Surveillance of Congenital Anomalies registry (EUROCAT). Distributions of CHD diagnoses within the Saudi Arabian dataset (Riyadh region and Saudi Arabia as a whole) were similar to those from these more comprehensive efforts, providing evidence for the completeness and accuracy of the CHD registry, for Riyadh region in particular. Secondly, an unmatched case-control study of risk factors for all structural congenital heart defects in children resident in Riyadh, Saudi Arabia was undertaken. The primary exposure of interest was consanguinity up to and including third cousins. Incident cases were identified from the CHD Registry from June 1, 2002 to December 31, 2004. Controls were obtained from the Well Baby Clinic, Riyadh Anned Forces (Military) Hospital. Using a detailed and reverse translated questionnaire, a face to face interview was conducted with 235 case and 247 control mothers by research assistants fluent in the local dialect. Mothers were asked to consider their exposure to risk factors within the period of 3 months prior to and 3 months post conception. Consanguinity was collected by phylogram method. The majority of mothers were interviewed when the infant was less than one year of age. Analyses were conducted using four different case groups: all cases, isolated cardiac cases, and embryological earliest and latest cases. Twenty five percent of cases and controls were first cousins or closer. Sixteen percent of cases versus 13 percent of controls were first cousins once removed or equivalent and 12 percent of both cases and controls were second 01' third cousins. Consanguinity was not found to increase the risk of CHD in this population. The adjusted odds ratio for all cases was 1.0 (CI9S=O.7-1.7) and for isolated cardiac cases it was 1.2 (CI9S=O.7-2.0). Statistically significant associations were found for other exposures such as previous pregnancy losses, maternal age, multiplicity, maternal use of hair dyes and pesticides sprayed in the house, confirming findings from previous studies. It is unlikely that the findings for consanguinity can be explained by misclassification of exposure or, in the analysis of all cases, low statistical power.