BACKGROUND: Head-and-neck squamous cell carcinomas (HNSCC) exhibit significant variations in incidence and outcomes across age groups. There is conflicting data on the oncological outcomes of younger HNSCC patients ≤ 45 years. This study analyzed clinical characteristics, treatment-related toxicities and survival rates of young HNSCC patients treated with (chemo)radiotherapy. METHODS: HNSCC patients ≤ 45 years treated with radiotherapy between 2009 and 2021 at two large cancer centers were analyzed and matched to a patient cohort > 45 years based on TNM and tumor localization. Overall (OS), progression-free (PFS) and metastasis-free (DMFS) survival and locoregional control (LRC) were compared and treatment-related toxicities were assessed. RESULTS: 99 patients were included in this analysis. Median OS of the young HNSCC cohort was 63 months. Daily alcohol consumption was identified as a key risk factor for reduced OS in the multivariate analysis. OS was similar in the young cohort compared to older patients, although the excess mortality risk compared to the sex- and age-matched general population amounted to 59-fold, while it was only 5.9-fold for patients ≥ 45 years. No significant differences were observed in PFS, LRC, or DMFS between age groups. Higher-grade chronic toxicities were moderate in young HNSCC patients. CONCLUSIONS: Young HNSCC patients ≤ 45 years treated with (chemo)radiation have similar rates of oncological survival outcomes compared to older patients. While chronic toxicities from (chemo)radiation are low, further research is needed to explore the long-term quality-of-life.