The cause of a seventeen-year-old female patient with septo-optic dysplasia and pituitary dwarfism is presented. Mental retardatin and epilepsy, in addition to absence of the septum pellucidum, point to a widespread lesion of the central nervous system. There is unilateral hypoplasia of the optic nerve. She is of small stature. The dynamic pituitary tests point to deficiency of GH, TSH and ACTH, and an adequate reserve of prolactin, gonadotropins and vasopressin. TSH insufficiency is probably of primary pituitary origin.