A boy referred at the age of 4 years because of obesity and under observation for 16 years, was found to be suffering from a hypothalamic syndrome of unknown origin characterized by progressive obesity, polyphagia, deficiency of growth and thyroid hormone, hyperprolactinemia, hypodipsia, hypernatremia and hyperosmolality without diabetes insipidus. At ages 11 and 16 there were 3 day episodes of spontaneous muscular weakness, hypersomnolence and hypothermia associated with central sleep apnea and severe bradycardia. Subsequently, decreased ventilatory responsiveness to carbon dioxide (CO2) was found as a consequence of blunted neural drive. Therapy with clomipramine HCl (Anafranil Ciba-Geigy) for 6 months led to a normalization of serum sodium levels, pulse rate, ventilatory response to dioxide with no recurrence of the central apnea within 4 following years.