The prevalence, incidence and clinical course of viral hepatitis were prospectively determined in consecutive recipients of T-cell depleted hematopoieic stem cell transplants (49 mismatched, 60 matched, mean age 38 years; range 11-65). The prevalence of hepatitis B virus (HBV) was 15.6% and that of hepatitis C virus was 3.7% (HCV). HBV reactivated in one patient. Another developed ex novo acute hepatitis B which progressed to chronic hepatitis. There were no new cases of hepatitis C or worsening of pre-transplant HCV infections. HBV and HBC did not affect the outcome of T-cell depleted hematopoieic stem cell transplantation. Surveillance is important given the risk of HCV and HBV infection and/or reactivation and the efficacy of the new anti-hepatitis drugs.