This is a report of a long term prospective study of 13 seriously ill patients with Budd-Chiari syndrome as a result of occlusion of the hepatic veins who were treated by side to side portacaval shunt from four to 78 weeks after the onset of symptoms and who were under observation for three to 16 years. The patient population was young, ranging in age from 19 to 45 years; seven were men and six were women. The presumed cause was the use of oral contraceptives in three, polycythemia rubra vera in two, Behcet disease in one patient and unknown in seven patients. All of the 13 patients had abdominal pain, marked ascites, hepatosplenomegaly, wasting and disturbed liver function. Diagnosis was based on the symptoms and signs: angiographic demonstration of hepatic vein occlusion and a patent inferior vena cava; pressure measurements that showed an inferior vena caval pressure that was normal or within the usual range for patients with massive ascites and an elevated wedged hepatic vein pressure that was much higher than the inferior vena caval pressure, and the results of biopsy of the liver showing centrilobular congestion and necrosis. Side to side portacaval shunt was very effective in decompressing the liver, reducing the mean corrected portal pressure from 240 millimeters of saline solution before to 7 millimeters of saline solution after the shunt. Operative survival rate was 92 per cent, and the long term survival rate for three to 16 years is 85 per cent. All of the survivors are free of ascites without requiring diuretic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)