The article describes two methods used to reveal possible teratogenic factors involved in the aetiology of abdominal wall defects. Forty-six mothers to children with gastroschisis and omphalocele were questioned about heredity, occupation, use of drugs etc. during early pregnancy (case history study). Seventy-four mothers to children with gastroschisis and omphalocele were randomly selected from a national register and their maternal health service record forms were studied and compared with the forms of 144 matched controls (case control study). None of the analyzed factors was found to be of significant teratogenic importance in the aetiology of abdominal wall defects, nor was it possible to explain the increase in the incidence of gastroschisis taking place during the early 70s.