Schmidt's syndrome (thyroid and adrenal insufficiency) and concurrent diabetes mellitus represent an intriguing multiple endocrinopathy in children. This report describes an eleven-year-old girl with diabetes of eight years' duration presenting in adrenal crisis. Serum thyroxine was undetectable, and antibodies to both thyroglobulin and adrenal tissue were found in high titer. The child's condition stabilized with hormonal replacement therapy, except for persistent growth failure. Approximately two years later she succumbed during a rapidly fulminant episode of ketoacidosis. The natural history of her illness supports recent speculation based on serologic data that juvenile diabetes mellitus may be an immunologic disorder in some children.