We studied the neurologic abnormalities in 41 men with isolated hypogonadotropic hypogonadism. Findings included anosmia, hyposmia, mirror movements, ocular motor abnormalities, cerebellar dysfunction, and pes cavus foot deformity. One-third of the subjects had a family history of delayed sexual maturation. Patients with a family history of delayed sexual maturation had a significantly higher incidence of olfactory dysfunction, mirror movements, and pes cavus foot deformity. Our data suggest that isolated hypogonadotropic hypogonadism and its accompanying neurologic abnormalities may arise from a genetically linked developmental abnormality of CNS structures.