Gastric adenocarcinoma developed in a 33-year-old homosexual man with human immunodeficiency virus (HIV) infection. This type of cancer is very rare in a man of his young age and in the absence of other factors. The tumor was aggressive and led to rapid death. Whereas Kaposi's sarcoma and lymphomas have been associated with HIV, there are only a few documented cases of adenocarcinoma associated with a suppressed immune system. The association between HIV infection and the virulence of this tumor appears to be strong.