The epidemiological, teratological and genetic data on 134 index patients with omphalocele (79 isolated and 55 multiple ones) and on 134 matched controls born in Hungary 1970-1976 were studied medical records and by retrospective interview. The stillbirth rate and infant mortality are significantly higher, and there is intrauterine weight retardation and more frequent preterm delivery. The distribution of maternal age-groups shows a 'U-shaped' trend in isolated omphalocele. Spontaneous abortions were significantly higher, particularly in previous pregnancies of mothers of index patients. A striking higher incidence of early and late toxaemia was found in the pregnancies of mothers of the isolated omphalocele group. Sib occurrence was not found in 161 brothers and sisters. Thus amniotic fluid AFP examination is not recommended in subsequent pregnancies. The occurrence of other congenital abnormalities corresponds to 'random' risk.