The aim of this study was to describe the influence of HIV infection on the staging of gastric cancer by using positron emission tomography/computed tomography (PET/CT) imaging. We treated a patient with local advanced gastric cancer. PET/CT showed an unusual hypermetabolic activity of lymph nodes, and the patient was later found to be HIV-positive. PET/CT scans in cancer staging of patients with chronic HIV infection may show advanced stage disease. Spread of primary tumor to unusual sites should be a warning sign for the possible concurrent diseases.