Two main types of abdominal wall defects were studied, omphalocele (n=133) and gastroschisis (n=194). Low maternal age was associated with a low risk for omphalocele but a high risk for gastroschisis. For both types of malformation the risk at parity 1 was higher than at higher parity. Maternal smoking was associated with gastroschisis – an increased risk was seen also for omphalocele but it was not statistically significant. A low body mass index was associated with an increased risk for omphalocele but not for gastroschisis. A period of unwanted childlessness seemed to ”protect” against gastroschisis but this observation was based on only three cases against nine expected. No statistically significant association with maternal drug use in early pregnancy was seen.