The clinical, surgical, laboratory and histological data of 237 children with extrahepatic biliary atresia were reviewed. Forty-seven patients (20%) had associated congenital anomalies, and of these, 28 had cardiovascular, 22 digestive and 19 splenic malformations. Of the 19 patients with splenic malformations, 13 showed the polysplenia syndrome and two had asplenia. Chromosome studies were performed in eight children, six having associated anomalies, and two of them showed karyotype abnormalities (46,XX,del 18 p- and 49,XXXXY). These observations indicated that biliary atresia could be subdivided into four distinct etiopathogenic subgroups, three involving a congenital form that could arise through a malformation, a disruption or a chromosome abnormality, and the remaining to agents active in the perinatal period (the acquired form). The surgical outcome in 171 patients operated on by an experienced surgeon was not influenced by the presence of anomalies but by the timing of surgery. Seventy-one percent of 24 patients operated on by 8 weeks of age were jaundice-free as opposed to only 34% of those who had later surgery (p less than 0.01).