The number of older patients with cancer is increasing as a result of the ageing of Western societies. Immune checkpoint inhibitors have improved cancer treatment and are associated with lower rates of treatment-related toxicity compared with chemotherapy in the general population. Nonetheless, immune checkpoint inhibitors have potentially serious immune-related adverse events, which might have a greater impact on older and more vulnerable patients and potentially influence treatment efficacy and quality of life. Previous clinical trials have shown no major increase in immune-related adverse events; however, older patients are underrepresented and relatively healthy in these trials. Observational studies suggest that older and more vulnerable patients may be at a higher risk of immune-related adverse events and early treatment discontinuation. Geriatric assessment could help identify older patients who will benefit from immune checkpoint inhibitors.