We report on two female adolescents--both diagnosed with type 1 diabetes mellitus in early childhood--who presented with signs of severe metabolic decompensation. In both cases recompensation was difficult, and during the stay in hospital increasing discoloration of palmar creases was observed. ACTH testing demonstrated cortisol deficiency in both patients. In addition, autoimmune thyroiditis was diagnosed in one patient. As a polyglandular autoimmune syndrome was suspected, autoantibody studies were performed and the presence of autoantibodies against thyroid and adrenal tissue was established. Polyglandular autoimmune syndrome (PGA) type II can lead to subsequent manifestation of deficiencies of several endocrine glands. Although PGA type II usually presents at a more advanced age, adolescents may also present with the full spectrum of the disease. Especially in the presence of Addison's disease, life-threatening situations can develop rapidly. Coloration of palmar skin creases of patients with known type I diabetes mellitus should serve as a warning sign to be followed up with investigation of endocrine functions.