Of 145 patients with severe aplastic anemia (SAA) treated in Basel from 1976 to 1987, 34 underwent bone marrow transplantation (BMT) and 111 received ALG therapy. We have analyzed the incidence of late complications in both groups of patients. 34 patients treated with ALG developed a hematological complication, 10 a myelodysplastic syndrome (MDS) and 18 paroxysmal nocturnal hemoglobinuria (PNH) associated with clinical symptoms in 12. Two patients had both MDS and PNH. Eight suffered relapse of SAA. After BMT neither of these complications occurred. Most of the non-hematological problems were associated with therapy. In the ALG group androgens were responsible for impotence and gynecomastia in men, deep voice in women and liver tumors in 4 patients. Four other patients developed aseptic necrosis of the hip and one carcinoma of the breast. The most severe late complication after BMT was chronic graft-versus-host disease (GvHD), occurring in patients still receiving methotrexate for prophylaxis of GvHD.