A majority of cancer cases now occur among older people, but this group is less likely to receive treatment and outcomes are poorer than in younger people. Age by itself can be a poor predictor of who will benefit from treatment with surgery, chemotherapy or radiotherapy. Comprehensive geriatric assessment is a multidisciplinary, multidomain process that helps to identify frailty, which is associated with increased mortality. Comprehensive geriatric assessment highlights areas that should be optimized before treatment and helps support a shared decision-making approach. Geriatricians, oncologists and surgeons now work together to help assess and support older people with cancer.