The association of gastric Kaposi's sarcoma (KS) with human herpesvirus type 8 (HHV-8) may be found in immunosuppressed patients such as those with AIDS or transplant recipients. A 64-year-old man with a 2-year history of corticosteroid treatment was admitted due to the impression of chronic obstructive pulmonary disease with secondary infection. Abdominal fullness and tarry stool led to the performance of panendoscopy, which revealed two hypertrophic gastric mucosal lesions. These lesions had transformed into a large polyp 2 months later. KS was not diagnosed until a third endoscopic biopsy was performed. The polyp further transformed into a flattened, elongated tumor within a month. The patient died from acute cardiopulmonary insufficiency 4 days after radical gastrectomy. Polymerase chain reaction study identified HHV-8 in all biopsied specimens and resected tumor lesions. Immunostaining further demonstrated the virus in the tumor cells. Both of these methods seemed more sensitive in diagnosing KS than histologic examination of small biopsied specimens. This case suggests the existence of a relationship between gastric KS and HHV-8 infection.