The overall landscape of health-related quality of life (HRQoL) has not been thoroughly investigated in adolescents and young adults (AYAs) with cancer. Data are also lacking on how well HRQoL at the time of cancer diagnosis can prognosticate long-term survival in AYA survivors. We included 3,497 survivors of AYA cancer (age 15-39 years at diagnosis) who completed the Short-Form 12 Health Survey (SF-12) HRQoL questionnaire at diagnosis. Physical component summary (PCS) and mental component summary (MCS) scores were generated, with scores <50 representing poor HRQoL. Differences in HRQoL by patient characteristics and tumor type were investigated using violin plots and t tests/analysis of variance. The effect of HRQoL on overall survival was assessed using Kaplan-Meier plots and Cox proportional hazards models. Overall mean PCS and MCS scores in this racially/ethnically diverse cohort (64% White, 19% Hispanic, 10% Black, and 7% other race/ethnicity) were 43.6 and 46.7, respectively. Women with breast cancer reported the most favorable PCS (50.8), and those with cervical cancer reported the lowest MCS (42.8). Age at diagnosis was associated positively with PCS (P<.001) and inversely with MCS (P<.001). Females had higher PCS yet lower MCS than males (both P<.001). Marginalized racial and ethnic populations reported lower PCS than White patients (P<.001). Physical and mental HRQoL were prognostic and associated with increased risk of poor survival (hazard ratio, 1.95; 95% CI, 1.72-2.21 for physical HRQoL, and 1.26; 95% CI, 1.13-1.40 for mental HRQoL). Physical and mental HRQoL at diagnosis vary across patient characteristics in AYA cancer survivors. Poor HRQoL at diagnosis may be a prognosticator of diminished overall survival among AYA cancer survivors.