OBJECTIVE: This study aimed to explore whether young adults with cancer have different functioning compared to older age groups with cancer. METHODS: This study is a cross-sectional study including 654 adults (≥18 years) with cancer. Exposure was age groups categorised as (1) young adults (n = 121) = 18-39 years; (2) middle-aged adults (n = 406) = 40-64 years; and (3) older people (n = 127) = ≥65 years. Outcomes were physical, role, social and cognitive functioning. Analyses consisted of linear regression models. RESULTS: Middle-aged adults had a statistically significant worse physical functioning compared to young adults (-3.90: [95% CI: -6.84; -0.95]). The older age group also had a statistically significant worse physical functioning compared to young adults (-7.63: [95% CI: -11.29; -3.96]). Young adults had statistically significant lower role functioning (-7.11: [95% CI: -1.13; -13.08]) and cognitive functioning (-13.82: [95% CI: -7.35; -20.29]) compared to the older age group. There was no statistically significant difference in social functioning between the age groups. CONCLUSION: Young adults with cancer seem to have other functioning problems compared with higher age groups. These findings support current research regarding the need to develop age-specific and appropriate rehabilitation services for young adults with cancer.