We evaluated the efficacy and long-term outcomes of immunosuppressive therapy (IST) in 50 adult patients with aplastic anemia at a single institution. Twenty-one patients who had not responded to the first course of IST or relapsed after the initial response to IST were retreated with the second course of IST with antithymocyte globulin. The response and relapse rate of the initial IST were 76.7% and 23.3%, respectively. The response rate of salvage IST was 61.9%. Overall survival at 10 years was 84.0%. Failure-free survival at 10 years was 62.0%. Clonal or malignant diseases developed in 2 patients. Early deaths due to bleeding or infection were observed only in elderly patients. We conclude that most patients with aplastic anemia treated with IST show hematologic improvement and excellent long-term survival.