We sought to determine if necrosectomy can be omitted for complicated acute necrotizing pancreatitis (ANP). Since 1996, we prospectively performed retroperitoneal drainage by introducing a sump drain to the pancreatic head area via a small left flank incision without debridement and irrigation on 19 consecutive complicated ANP patients. We purposely delayed surgery until liquefaction of retroperitoneal tissue reached the left flank. Our patients had a mean Ranson's and APACHE II score of 5.9 (range, 4-8) and 20.1(range, 4-45), respectively. Sixteen available CT showed retroperitoneal liquefaction after 21.3 days (range, 14-26). Operations were delayed for 4.7 weeks (range, 1.3-9.0). No patient succumbed during this period. The indications were infected necrosis in 16 and severe abdominal pain/food intolerance in 3 patients. Average skin incision was 4.0 cm (range, 3-9). Fungi or bacteria were cultured in 15 patients (80.0%). The recovery courses were surprisingly uneventful. Oral intake began within 2.4 days (range, 1-5) and mean hospital stay (16 survivals) was 23.2 days (range, 4-120) after operation. Drains were completely removed 120.6 days (range, 60-250) later from these outpatients. One gastric perforation and one minor duodenal leak were the only procedure-related complications (10.5%). Three patients died (15.8%), although one had a healed ANP. In conclusion, this delay-until-liquefaction strategy without necrosectomy is an easy and effective treatment method.