A 37-year-old male was presented with an upper abdominal mass. A retroperitoneal bulky tumor was detected and operative biopsy revealed seminoma. The right testis was undescended and atrophic which was located at the left inguinal lesion. Pathologically, the primary tumor cells were not found in the left orchiectomied testis, but only scar and fibrosis were compatible with a burned-out testicular tumor. This patient showed partial regression by multidisciplinary therapy including combined chemotherapy with CDDP, etoposide and peplomycin, and is still on the same condition and alive for 3 years. In case of extragonadal germ cell tumor without apparent testicular involvement, it is a problem to differentiate primary extragonadal germ cell tumor from occult and burned-out testicular tumor. Testis should be examined by all means available including careful exploration.