We conducted a retrospective study to investigate the incidence, risk factors, and clinical features of hemorrhagic cystitis (HC) following allogeneic hematopoietic cell transplantation (allo-HCT). Adult patients who developed HC after allo-HCT were identified from the HCT database of the Asan Medical Center and their medical records were reviewed. From December 1993 to August 2001, a total of 210 adult patients underwent allo-HCT. Fifty-one patients developed HC with a cumulative incidence of 25.7%. The median onset of HC was post-transplant day 24 (range, -2 to 474), and the median duration was 31 days (range, 8 to 369). Significant risk factors for HC by univariate analysis included diagnosis of chronic myelogenous leukemia (p=0.028), unrelated HCT (p=0.029), grade III-IV acute graft-versus-host disease (GVHD) (p<0.001), extensive chronic GVHD (p=0.001), and positive cytomegalovirus antigenemia between post transplant days 31 and 60 (p=0.031). Multivariate analysis showed that grade III-IV acute GVHD was the most important risk factor for the occurrence of HC after allo-HCT (odds ratio, 3.38; 95% CI, 1.36-8.39). Late-onset HC, which occurred beyond 3 weeks after allo-HCT, was more frequently associated with GVHD than earlyonset HC (p=0.007). Our data suggest that a portion of late-onset HC might be a manifestation of GVHD.