Idiopathic acquired pure amegakaryocytic thrombocytopenic purpura (APATP) in young patients (non-neonates) is a rare disorder with a variable clinical course. Cure is unusual. A 13.5-year-old boy with idiopathic APATP was treated with cyclosporin A. Apparently effective, the treatment resulted in the reappearance of marrow megakaryocytes and normalization of platelet count.