PurposeThis study examines posttraumatic growth (PTG) among adolescents and young adults (AYAs) with cancer, as well as its correlates and trajectories over time. The study also explores the buffering role of PTG on the associations between posttraumatic stress (PTS), health-related quality of life (HRQoL), and psychological distress.MethodsA multicenter, longitudinal, prospective study was conducted among AYA cancer patients aged 14–39 years. One hundred sixty-nine patients completed a self-report measure of PTG (PTGI) and PTS (PDS) 6, 12, and 24 months after baseline (within the first 4 months of diagnosis). At 24-month follow-up, HRQoL (SF-36) and psychological distress (BSI-18) were also assessed.ResultsAmong participants, 14% showed increasing PTG, 45% remained at a stable high PTG level, 14% showed decreasing PTG, and 27% remained at a stable low PTG level. AYAs who remained high on PTG were more often younger, female, and received chemotherapy. PTG level at 6-month follow-up was predictive of mental HRQoL (β = 0.19; p = 0.026) and psychological distress (β = −0.14; p = 0.043) at 24-month follow-up when corrected for PTS and sociodemographic and clinical covariates. No relationship between PTG and physical HRQoL was found. The interactive effects of PTS and PTG on outcomes were not significant, indicating that buffering did not take place.ConclusionThis study indicates that PTG is dynamic and predicts mental well-being outcomes but does not buffer the effects of PTS. Psychosocial interventions should focus on promoting PTG and reducing PTS in order to promote the adjustment of AYAs diagnosed with cancer.