The availability of longitudinal data collected prospectively from 1998 to 2011 at federally funded US hemophilia treatment centers provided an opportunity to construct a descriptive analysis of how outcomes ofmenwith severe hemophilia have been altered by the incremental advances and setbacks in hemophilia care in the last 50 years in the United States. This surveillance collaboration with the US Centers for Disease Control and Prevention assembled the largest uniformly examined population with severe hemophilia (n = 4899 men with severe factor VIII and IX deficiency). To address the heterogeneity of this population, 4 successive birth cohorts, differentially affected by eras of hemophilia care, were examined separately in regard to demographics, complications of hemophilia and its treatment, and mortality. Severely affected men in each birth cohort were compared also with the corresponding mild hemophilia birth cohorts (n = 2587 men total) to control for outcomes that might be attributable to aging and environment independent of severely defective hemostasis. The analysis demonstrates improving access to standard of care therapy, correlating the proportion of men on prophylactic factor replacement and reduced bleeding frequency for the youngest men. Frequent bleeding persisted in one third to one half of men across all ages, however, and the disability gap between severe and mild hemophilia did not narrow. The greatest cause of death was liver failure, but attempted anti-hepatitis C virus therapy and cure were low. The study suggests a continued need for national surveillance tomonitor and informhemophilia interventions and outcomes.