Patients with acquired immune deficiency syndrome (AIDS) are susceptible to secondary malignant tumors. Among those malignancies, the increased incidence of germ cell tumor (GCT) in patients with AIDS has recently been documented in Western countries, while that is still rare in Japan. Here, we report a man patient with advanced GCT (seminoma) complicated with AIDS who was continuously treated with highly active antiretroviral therapy (HAART). A partial response was obtained after resection of the primary left testis and three courses of chemotherapy. During the clinical course, he contracted unexpected gastric bleeding that made it impossible to take HAART agents and prophylactic agents for opportunistic infection. Thereafter, he suffered from a severe pulmonary infection and consequently died of severe respiratory failure. The lymphopenia related to both chemotherapy and AIDS synergistically rendered this patient immunoincompetent and thus he suffered from this fatal pulmonary infection. The recent progress in AIDS treatment has been reported to prolong the survival of tumor-bearing AIDS patients, especially GCT-bearing AIDS patients. Because of the current increase in the number of AIDS patients in Japan, it is important to report the present case which indicated that careful chemotherapy against GCT with strict management of the immunoincompetence can provide a good prognosis for GCT-bearing AIDS patients.