History and admission findings: A 22-year-old man was admitted in a severely reduced condition. Type 1 diabetes mellitus had been diagnosed when he was 13 years old, hypothyroidsm was treated with L-thyroxine for 2 years. For the past 3 years he suffered from repetitive hypoglycemia, combined with vertigo, weakness and low blood pressure. Investigations: He presented with hypotension and hyperpgimentation of the skin. Pathological laboratory results were: serum creatinine 2.5mg/dl; urea 145mg/dl; sodium 124 mmol/l; potassium 8,3 mmol/l, HbA(1c) 9.1%. The ECG showed large T waves. Additionally, plasma aldosterone was decreased (<10ng/l), plasma renin was increased (2404ng/l), basal serum cortisol was decreased (16,1 mug/l). No increase of plasma cortisol after i.v. stimulation with ACTH (1-24) occurred. Plasma ACTH was increased to 630 pg/ml. Test for adrenal autoantibodies were positive. Diagnosis: Primary adrenal insufficiency with prerenal renal failure. Autoimmune polyglandular syndrome (APS) type 11 with Addison's disease, diabetes mellitus type 1 and hypothyroidism (Schmidt-Carpenter-Syndrome) were diagnosed. Treatment and course: Initially, the patient was treated with sodium chloride 0.9% i.v. and oral sodium 5 g 4 times/day. In addition, he was given hydrocortisone 100mg i.v., and then switched to 40mg per day (20-10-10mg), fludrocortisone 0.05mg/day and L-thyroxine 75 mug/day orally the clinical condition improved dramatically within 24 hours. Intensified conventional insulin therapy was continued. Conclusion: In patients with type 1 diabetes, especially in combination with associated organ-specific autoimmune diseases, autoimmune polyglandular syndrome should be considered and adequately treated with those hormones that are reduced.