Thirty-six consecutive patients with massive tissue necrosis resulting from acute pancreatitis were initially managed nonoperatively. In each instance, a mass of necrotic tissue, bathed in fluid, became evident. Laparotomy was delayed unless a life-threatening complication developed. In no instance did the "cavitary necrosis" disappear prior to laparotomy. In five patients, laparotomy was avoided and a chronic pseudocyst evolved. Thirty-one patients required laparotomy, usually after a lapse of one to two months. The necrotic tissue was always retroperitoneal and was clearly demarcated from viable tissue. In most instances, the necrotic tissue was predominantly retroperitoneal adipose tissue. Under such conditions, the anatomic definition of the pancreas, per se, was not practical. The preoperative and operative diagnosis of secondary infection of the necrotic tissue was often difficult. The operation consisted of necrosectomy (débridement) and external drainage. The amount of necrotic tissue was often in excess of 1 kilogram. When necrosectomy was incomplete, secondary explorations and débridement were sometimes necessary. In retrospect, in only a few instances did necrosis and necrosectomy appear to have resulted in the loss of an appreciable amount of pancreatic tissue. One of the 36 patients died, giving a mortality rate that compares favorably with reports of earlier operative intervention.