A new-born baby with Beckwith's syndrome had severe hypoglycaemia, and was treated with glucagon and prednisone. Treatment was stopped at 1 month of age and his blood glucose levels were satisfactory for the ensuing 6 weeks. However, at 10 weeks of age, he had a hypoglycaemic convulsion and required large doses of diazoxide and prednisone for the next 2 months to maintain the blood glucose above 40 mg/100 ml. Insulin excretion was raised until he was 4 months old. Cases of Beckwith's syndrome which develop hypoglycaemia, should be treated with diazoxide and corticosteroids until insulin excretion is normal.