One hundred ten of 175 patients with aplastic anemia conditioned by cyclophosphamide had sustained engraftment of marrow from human leukocyte antigen (HLA)-identical siblings and lived for more than 6 months. Forty-nine of the 110 patients developed chronic graft-versus-host disease between 85 and 464 days. Ninety-seven patients are alive from 1.4 to 11 years after engraftment; 13 died between 208 and 726 days. Twenty of the 36 surviving patients with chronic graft-versus-host disease have Karnofsky performance scores of 100%, 7 of 90%, 5 of 80%, 1 of 70%, 2 of 60%, and 1 of 40%. Our analysis, using a binary logistic regression model, identified three factors predicting chronic graft-versus-host disease: moderate to severe acute graft-versus-host disease with an estimated relative risk of 11.65; increasing patient age; and the use of viable donor buffy coat cells in addition to the marrow to prevent graft rejection. The last two factors were significant only in patients without acute graft-versus-host disease.