During a 5-year period, 13 patients who presented with massive upper gastrointestinal hemorrhage had normal findings on arteriography. Seven had prophylactic embolization of the left gastric artery, and six had conservative therapy. Normal angiographic findings were associated with clinical cessation of bleeding in 12 of 13 patients. Lesions not treated by embolization or other invasive therapy had a high rate of massive recurrent hemorrhage (four of six). Of lesions subsequently found to be supplied by the left gastric artery, two of four cases not treated by embolization or surgery had clinically significant recurrent hemorrhage, whereas none of six cases treated by embolization had recurrent hemorrhage. Prophylactic embolization of the left gastric artery appears warranted when (1) there is definite prior identification of a lesion in the left gastric artery territory or (2) there is no prior localization of a lesion but the patient is at risk for multiorgan failure if bleeding recurs.