This study was conducted on 3212 Saudi families to investigate the prevalence of consanguineous marriages. The families were interviewed and the information on the relationship between the husband and wife was obtained. The overall rate of consanguinity shows that 57.7% of the families screened were consanguineous. The most frequent were first cousin marriages (28.4%) followed by distant relative marriages (15.2%) and second cousin marriages (14.6%). The families were grouped according to the province of their origin and the consanguinity rates were calculated accordingly. There were slight differences in the consanguinity rates in the five provinces, which ranged from 52.1% to 67.7%. In each province first cousin marriages were the most frequently encountered pattern, ranging from 17.9% to 40.9%. The inbreeding coefficient (F) was calculated for each province and ranged from 0.020 to 0.030. Within each province, there were several significant differences among the populations in the different areas. The highest rate of consanguinity was 80.6% in Samtah and the lowest rate was around 34% in Abha in the South Western province. These results place Saudi Arabia among the countries of the world with a high rate of consanguinity. The possible consequences of increased consanguinity are presented and discussed.