Objectives To examine subjective fatigue and sleepiness as predictors of functional outcomes in long-term pediatric hematopoietic stem cell transplant (HSCT) survivors. Methods Participants included 76 survivors assessed 5–14 years post-HSCT. Self-report and parent-proxy (i.e., N = 38) measures of fatigue, excessive daytime sleepiness (EDS), emotional and behavioral functioning, executive functioning, and quality of life (QOL) were completed. Health-related correlates were obtained from medical records. Results Survivors exhibited significant fatigue for self (M = 69.21 ± 20.14) and parent-proxy (M = 72.15 ± 20.79) report. EDS was endorsed for 20–33% of survivors, depending on the respondent. EDS was not significant for parent-proxy outcomes, but was associated with poorer self-reported QOL and internalizing problems (p < .0016). Fatigue was associated with poorer functioning across all domains (p’s < .0016). Conclusions A substantial number of pediatric HSCT survivors exhibit sleepiness and fatigue. Fatigue is associated with statistically and clinically greater functional difficulties, highlighting the importance of examining sleep and fatigue and considering interventions to improve alertness.