PURPOSE Geriatric assessment (GA) is a guideline-recommended approach to optimize cancer management in older adults. We conducted a cost-utility analysis alongside the 5C randomized controlled trial to compare GA and management (GAM) plus usual care (UC) against UC alone in older adults with cancer. METHODS The economic evaluation, conducted from societal and health care payer perspectives, used a 12-month time horizon. The Canadian 5C study randomly assigned patients to receive GAM or UC. Quality-adjusted life-years (QALYs) were measured using the EuroQol five dimension-5L questionnaire and health care utilization using cost diaries and chart reviews. We evaluated the incremental net monetary benefit (INMB) for the full sample and preselected subgroups. RESULTS A total of 350 patients were included, of whom 173 received GAM and 177 UC. At 12 months, the average QALYs per patient were 0.728 and 0.751 for GAM and UC, respectively (ΔQALY, −0.023 [95% CI, −0.076 to 0.028]). Considering a societal perspective, the total average costs (in 2021 Canadian dollars) per patient were $46,739 and $45,177 for GAM and UC, respectively (ΔCost, $1,563 [95% CI, −$6,583 to $10,403]). At a cost-effectiveness threshold of $50,000/QALY, GAM was not cost-effective compared with UC (INMB, −$2,713 [95% CI, −$11,767 to $5,801]). The INMB was positive ($2,984 [95% CI, −$7,050 to $14,179]; probability of being cost-effective, 72%) for patients treated with curative intent, but remained negative for patients treated with palliative intent (INMB, −$9,909 [95% CI, −$24,436 to $4,153]). Findings were similar considering a health care payer perspective. CONCLUSION To our knowledge, this is the first cost-utility analysis of GAM in cancer. GAM was cost-effective for patients with cancer treated with curative but not with palliative intent. The study provides further considerations for future adoption of GAM in practice.