Autologous blood or marrow transplantation (BMT) is a curative option for several types of childhood cancer. However, there is little information regarding the risk of late mortality. We examined all-cause mortality, relapse-related mortality (RRM), and nonrelapse-related mortality (NRM) in 2-year survivors of autologous BMT performed before age 22 between 1980 and 2010 at 1 of 2 US transplant centers. Vital status information was collected using medical records, National Death Index, and Accurint databases. Overall survival was calculated using Kaplan-Meier techniques. Cumulative incidence of mortality used competing risk methods. Standardized mortality ratio (SMR) was calculated using age-, sex-, and calendar-specific mortality rates from Centers for Disease Control and Prevention. Cox regression analysis was used to determine predictors of all-cause late mortality. Among the 345 2-year survivors, 103 deaths were observed, yielding an overall survival of 70.3% 15 years post-BMT. The leading causes of death included primary disease (50.0%), subsequent neoplasm (21.4%), and infection (18.2%). Overall, the cohort was at a 22-fold increased risk of late mortality (SMR, 21.8; 95% CI, 17.9-26.3), compared with the general population. Mortality rates remained elevated among the 10-year survivors (SMR, 20.6; 95% CI, 9.9-37.2) but approached those of the general population ≥15 years post-BMT. The 10-year cumulative incidence of RRM (14.3%) exceeded that of NRM (10.4%). The 10-year cumulative mortality rate declined over time (<1990, 35.1%; 1990-1999, 25.6%; 2000-2010, 21.8%; P 5 .05). In conclusion, childhood autologous BMT recipients have an increased risk of late mortality, compared with the general population. The late mortality rates have declined over the past 3 decades.