A 77-year-old man with diabetes mellitus presented with a 2-month history of lumbago radiating to the right lower limb as well as high fever spikes. Physical examination revealed a distended abdomen with right lower quadrant tenderness. A computed tomographic scan of the abdomen revealed a large right retroperitoneal cavity containing an air-fluid level that was consistent with a gas-producing abscess. The patient began receiving intravenous antibiotics, but fever and abdominal pain persisted and a large, fluctuating, tender swelling appeared on the medial aspect of his right thigh and right calf. The patient underwent surgical exploration: a right lateral abdominal incision was performed, and the pus collection in retroperitoneal space was completely evacuated. We also made 3 separate incisions on the medial aspect of the right thigh and 1 incision on the upper calf, resulting in the drainage of pus. The patient made a slow but steady recovery.