We report on two children with both Addison's disease and diabetes mellitus, a rare occurrence in children. One of the children first developed Addison's disease and later developed diabetes mellitus, while the other had the onset of diabetes mellitus first and later Addison's disease. In the latter patient a direct relationship was shown between the insulin dose and adrenal cortical hormone. Organ-specific antibody studies are reported and the diagnosis and management of these combined endocrinopathies are discussed.