Of 440 patients who underwent operative portal decompression to control variceal hemorrhage, 25 (6%) had histologically verified noncirrhotic portal hypertension (NCPH). A review of these patients identified two distinct patterns of disease. Fourteen children with an average age of 8.5 years were treated with no deaths at operation. Occlusion of the portal vein (PV) was demonstrated preoperatively or intraoperatively in 10 children (71%). Follow-up for 12 to 207 months showed that no children died of a liver-related illness and only one child (7%) developed portal-systemic encephalopathy (PSE). In contrast, 11 adults with an average age of 56 years were treated with an operative mortality rate of 18%. Occlusion of the PV was demonstrated angiographically in four adults (35%). Of nine surviving adults who were followed for 12 to 164 months, five adults (56%) manifested PSE. Intraoperative liver biopsy specimens were analyzed by light microscopy in all cases. With the possible exception of sinusoidal fibrosis and dilatation of intrahepatic portal venous radicles, no histologic discriminators of adult forms versus childhood forms were identified regardless of the status of the PV. We conclude that age stratification in patients with NCPH may provide important prognostic data regarding survival rates and the incidence of PSE after portal-systemic shunting.