The eye movement abnormalities in two men with isolated hypogonadotropic hypogonadism were studied clinically and electro-oculographically. Both demonstrated striking saccadic dysmetria. Subsequent neuroradiologic investigation confirmed atrophy of the cerebellar vermis in one of the patients. This is in concert with other midline structural abnormalities described in patients with isolated hypogonadotropic hypogonadism and suggests that this syndrome may arise from a genetically linked developmental abnormality of midline central nervous system structures.