Treatment of necrosis associated with acute pancreatitis is controversial. Forty consecutive patients (63.4 +/- 1.4 years of age) with necrotic retroperitoneal fat associated with nonalcoholic pancreatitis were treated by débridement and closed drainage. None of the patients had overt pancreatic necrosis. Eight percent of the patients were operated upon 48.4 +/- 2.9 days (late referrals) and 20 percent on 4.3 +/- 0.6 days after the onset of pancreatitis. The main indication for operation was clinical deterioration. All patients had bacterial infection of the necrosis and none had a preoperative invasive procedure. Twenty-five percent of the patients had colonic necrosis at initial operation; this did not progress thereafter. No patient had histologically identifiable pancreas, which remained grossly intact at the conclusion of operation. Morbidity included postoperative "septic shock" in 97.5 percent of the patients, renal failure in 40.0 percent and enterocutaneous fistula in 47.5 percent. Reoperation for a persistent septic focus was required for 25 percent of the patients. The mortality rate was only 2.5 percent. No patient operated upon early had colonic necrosis or postoperative worsening of renal function or a fistula or required reoperation. The outcome suggests that most patients with infected retroperitoneal fat necrosis do not require pancreatic resection. Open drainage or use of continuous lavage, or both, are not necessary to achieve a low mortality rate. Retroperitoneal necrosis can harbor infection much earlier than commonly believed. While mortality has not been clearly shown to be related to early or late débridement, early operation upon patients with infected necrosis may decrease the morbidity rate.