Five of 13 patients with microphthalmia or clinical anophthalmia studied in an institution of 650 mentally retarded adults had hypogonadotropic hypogonadism. Four males had low testosterone levels and sexual infantilism, manifesting as micropenis with small testes or cryptorchidism. One female had primary amenorrhea. All 5 patients had low gonadotropin levels, confirming a hypothalamic or pituitary basis for their hypogonadism. Thyroxin, thyroid stimulating hormone, prolactin, and A.M. cortisol were also measured and were normal. All patients with hypogonadotropic hypogonadism were chromosomally normal and had variable central nervous system defects, suggesting that they comprise a heterogeneous group of disorders. Microphthalmia or anophthalmia in a mentally retarded patient is associated with hypogonadotropic hypogonadism.