Benign mediastinal teratoma associated with Klinefelter's syndrome.

We treated a patient with a benign mediastinal teratoma associated with Klinefelter's syndrome which was first thought to be a malignant germ cell tumor because of an anterior mass shadow, gynecomastia, atrophic testis and a high level of HCG. Chromosomal analysis showed a total of 47 XXY. Median sternotomy revealed a tumor originating from the right lobe of thymus. The postoperative course and 2 year follow-up have been uneventful.