Patients with Klinefelter's syndrome have an increased incidence of mediast
inal germ cell tumors(1) but testicular tumors are rare.(2) We describe tes
ticular teratoma in a man with the XX/XXY mosaic Klinefelter syndrome. To o
ur knowledge our case represents the first report of XX/XXY mosaic Klinefel
ter's syndrome associated with testicular teratoma.