A case of metachronous bilateral testicular seminomas on a 36-year-old male is reported. He had a history of right testicular typical seminoma treated with right high orchiectomy and adjuvant irradiation therapy 6 years previously. He returned to our clinic complaining of painless left testicular enlargement in August 1990, and under a diagnosis of testicular neoplasm left high orchiectomy was performed. Histopathological examination revealed anaplastic seminoma. DNA histograms of both testicles revealed almost the same aneuploid pattern. The patient was diagnosed as stage I seminoma, has been followed up closely. Recently genetic factors as human leukocyte antigens (HLA)-A24, B14, DR5 and DR7, have been shown to be important in the development of metachronous bilateral testicular tumors. HLA antigens were determined in our case, and HLA-A24 shown in our case was compatible with the review.