One hundred and seventeen patients undergoing allogeneic bone marrow transplantation (BMT) for severe aplastic anemia (n = 18) or leukemia (n = 99) who were alive on day +180, were analysed for the incidence and severity of chronic graft-versus-host disease (cGVHD), developing before or after discontinuation of cyclosporin A (CSA). All patients received CSA for GVHD prophylaxis for 94 to greater than 988 days post-BMT. cGVHD developed in 74 patients (63%) before CSA discontinuation (de novo n = 12, progression from acute GVHD n = 42, following resolution of acute GVHD n = 20). CSA was discontinued in 112 patients: electively (n = 80), because of toxicity (n = 8), or following relapse of leukemia (n = 24). In five patients CSA was never discontinued. After discontinuation of CSA, progression or de novo cGVHD was seen in 25 patients, with a significant difference in patients treated for more or less than 150 days (8% vs 41%, p = 0.0007). In 15 patients CSA had to be re-instituted and in 14 it could be discontinued a second time. Overall 111/117 (94%) patients have finally discontinued CSA. In conclusion cGVHD will progress or appear de novo in 41% of patients receiving CSA for less and in 8% of those receiving CSA for more than 150 days respectively, indicating that the drug should be administered for at least 5 months post-BMT. Most patients (94%) will eventually become CSA independent.