Cerebellar ataxia with hypogonadotropic hypogonadism is a rare condition. Both hypothalamic LHRH and pituitary gonadotropin deficiency may appear with cerebellar ataxia. In this report, a 19-year-old man who presented with progressive cerebellar ataxia and mental disturbance was found to have low plasma gonadotropin levels. No rise in gonadotropin was demonstrated after repeated stimulation with LHRH. Our findings suggested that the cause of hypogonadism was pituitary gonadotropin deficiency, or both hypothalamic and pituitary dysfunction. The endocrinological data and clinical features of our patient and all other reported cases suggest that the age of onset of the illness is related to the type of endocrinological abnormality: young-onset patients may have endocrine disturbances involving both the hypothalamus and the pituitary gland, which may be affected secondary to the hypothalamic disturbance, whereas adult-onset patients may show only hypothalamic disturbance.