We present a very rare case of a retroperitoneal extrarenal angiomyolipoma accompanied by early gastric cancer. A 41-year-old Japanese man, who had undergone surgery for a type IIc early gastric cancer 2 years earlier, was admitted to hospital presenting with back pain and abdominal fullness. Computed tomographic scanning and magnetic resonance imaging of the abdomen disclosed a massive fatty tumor extending from the hepatic hilus to the retroperitoneum. A large retroperitoneal tumor mass with no sign of involvement in the kidney was totally resected by radical surgery. Histologically, the tumor was classified as an angiomyolipoma.