Patients with brain damage, especially under malnutrition, sometimes show a disordered thermoregulation. Our case was an 11 year-3-month-old boy with severe brain damage probably of prenatal origin, who was physically extremely small in size for age and showed difficulty of taking food. Low body temperature ranging from 34.0 degrees C to 36.0 degrees C became outstanding since 9 years of age. Continuous rectum temperature monitoring was starged, when he was admitted in our department of pediatrics in Tokyo Women's Medical College Hospital for the therapy of acute infection. Before hospitalization, he took orally only 150 to 200 kcal/day. After the recovery from the infection, a higher calorie diet appropriate for his body weight was given through a nasal tube. Dramatic improvement was observed in terms of sleep pattern, body temperature and thermoregulation after the administration of higher calorie nutrients. It is suggested that the circadian rhythm of the body temperature would be disturbed by chronic malnutrition in children with brain damage.