A 21-year-old patient, since the age of 16, presented a familial type of chronic autoimmune thrombocytopenia that responded only partially to various types of immunosuppressive treatment. His prolonged survival, compared to his decreased siblings, was complicated by the appearance of a severe enteropathy. High doses of corticosteroids induced a type 1 diabetes as a major side effect. The introduction of cyclosporine resulted in both a continuous complete clinical remission and a partial hematological remission and allowed the discontinuation of all other medication for 18 months. In uncommon complex autoimmune disease, cyclosporine may represent a safe and effective alternate therapy when other immunosuppressive agents have failed.