Young adults (YA), age 18 to 39 years, are at a stage of life that may make them more vulnerable than older adults to impairments in health-related quality of life (HRQOL) during and after hematopoietic cell transplantation (HCT). Health self-efficacy (HSE), the belief that one can implement strategies to produce a desired health outcome, has been associated with health outcomes in oncology research. Little is known about HRQOL or HSE in YA HCT survivors compared with older HCT survivors. Given the age-specific psychosocial challenges facing YA HCT recipients and research on non-transplant YA cancer survivors, we hypothesized that YA survivors would have worse post-HCT HRQOL compared with older adults, and that among YA HCT survivors, higher levels of HSE would be associated with higher levels of HRQOL and lower levels of cancer-related distress. This was a cross-sectional secondary analysis of 2 combined baseline datasets from multicenter studies of HCT survivors approached for participation in clinical trials of survivorship interventions. Participants from 20 transplantation centers in the United States were at 1 to 10 years post-HCT and age ≥18 years at the time of study enrollment, had no evidence of disease relapse/progression or subsequent malignancies, and could read English adequately to consent for and complete assessments. Medical record and patient-reported data were obtained for demographics and HCT-related clinical factors and complications (eg, total body irradiation, chronic graft-versus-host disease [cGVHD]). Participants completed surveys on HRQOL, including the Short-Form [SF]-12, HSE, and Cancer and Treatment Distress (CTXD), which includes 6 subscales and reports an overall mean score. On the SF-12, both the Mental Component Score (MCS) and Physical Component Score (PCS) were calculated. Two cohorts were compared: YAs (age 18 to 39 years at transplantation) and older adults (age ≥40 years at transplantation). Multiple linear regression analyses identified factors associated with HSE, PCS, MCS, and CTXD in YAs. In this analysis of 979 survivors, compared with the older adults, the YA participants had lower median mental health scores (SF-12 MCS: 48.40 versus 50.23; P=.04) and higher cancer-related distress (CTXD: .96 versus .85; P=.04), but better physical health (SF-12 PCS: 48.99 versus 47.18; P=.049). Greater overall cancer-related distress was driven by higher levels of uncertainty, financial concern, and medical demand subscales for YAs compared with older adults. Young adults also had lower HSE (2.93 versus 3.08; P=.0004). In a multivariate model, HSE was strongly associated with age group (P=.0005) after adjusting for multiple other transplantation-related factors. Among YAs, HSE was associated with the SF-12 MCS and PCS and the CTXD, and HSE remained significant after adjusting for other transplantation-related factors. Overall, the YA HCT survivors had lower mental health, increased cancer-related distress, and lower levels of HSE compared with the older adults. Although the direction of these effects cannot be determined with these data, the strong association between HSE and HRQOL among YAs suggests that targeting interventions to improve HSE may have broad impact on health outcomes.