We examined the clinical literature on congenital abdominal wall defects to confirm our impression that gastroschisis had become more common than omphalocele. We then examined the teratology literature and noted that congenital abdominal wall defects were frequently induced by teratogens. This lead us to review the antenatal history of 19 infants with gastroschisis and 54 control infants born with a congenital anomaly unrelated to gastroschisis. When compared to controls, mothers of infants with gastroschisis were more likely to have used aspirin during pregnancy and to have been taking oral contraceptives at the time of conception. Additionally, an increased incidence of illegal drug use (particularly cocaine) was noted among the study mothers. We conclude that gastroschisis is becoming the more common congenital abdominal wall defect, and that it could be related to exposure to an environmental teratogen.