Since 1980, 107 consecutive patients (pts) underwent bone marrow transplantation (BMT) for nonconstitutional severe aplastic anemia (SAA) at our institution. All received conditioning with Cytoxan (150 mg/kg) and thoraco-abdominal irradiation (6 Gy) from an HLA-identical sibling donor. Mean age was 19 years (5 to 46 years). Forty-nine pts had less than 0.2 x 10(9)/L PMN and 53 failed to respond to previous immunosuppressive therapy before BMT. Graft-versus-host disease (GVHD) prophylaxis consisted of methotrexate (22 pts), cyclosporine (52 pts), or both (33 pts). With a median follow-up of 45 months (12 to 120 months), overall actuarial survival was 68% (confidence interval 95%:9.7). Of 16 factors tested, five were shown to adversely influence survival by multivariate analysis: grade greater than or equal to 2 acute GVHD (relative risk [RR]: 5.5), prior immunosuppressive therapy (RR: 3.5), female as donor (RR: 2.4), nonidiopathic SAA (RR: 2), and more than 0.2 x 10(9)/L PMN AA (RR: 2). Because acute GVHD was the most potent factor for survival, we analysed risk factors for acute GVHD. By multivariate analysis, 2 of 14 factors tested were independent: male as recipient (RR: 3) and previous alloimmunization of the donor (RR: 4.3). On long-term follow-up, chronic GVHD was observed in 49 pts of 89 surviving more than 100 days (55%). Multivariate analysis showed that infection before transplant (RR: 1.3) and previous history of acute GVHD (RR: 1.8) were associated with an increased risk of chronic GVHD.