Portal branch ligation, a new surgical treatment for unresectable carcinoma of the liver, was performed in twenty patients. All the patients tolerated the procedure, and morbidity and mortality were minimal, even in patients in poor general condition. The responses to ligation differed considerably, but significant palliation was attained in some patients and one survived six years. The effect of portal branch ligation on the tumor appears to be closely related to the degree of tumor vascularity, tumor malignancy, and portal circulatory disturbances such as cirrhosis, portal hypertension, or portal thrombosis. We believe that the present procedure can be recommended for clinical application in some patients with unresectable carcinoma of the liver.