47,XXY Klinefelter's syndrome with low FSH and LH levels and absence of Leydig cells.

Examination of testicular biopsy from a patient with 47,XXY Klinefelter's syndrome revealed a diffuse hyalinization of seminiferous tubules as well as absence of mature Leydig cells. Ultrastructural findings showed some immature Leydig cells in the testicular interstitium. Hormone assays revealed low serum FSH and LH levels. The association of both, hormone assays and testicular morphologic pattern, suggests the presence of a Klinefelter's syndrome with hypogonadotropic hypogonadism.