The incidence of both cancer and cognitive impairments from various origins increases with age. Oncologists are increasingly being confronted with cancers occurring in patients with cognitive impairment, yet very few studies have addressed the problem. Cognitive impairment affects a patients' survival to an extent similar to an average cancer, and this can be an important thing to consider, especially in the adjuvant setting. Cognitive impairment also predisposes patients to delirium in the surgery setting or during hospitalization. Because effective preventive measures exist, careful attention should be paid to identifying patients at risk. Cognitive impairment does not automatically mean inability to consent, but particular precautions should be taken. For outpatient treatments such as chemotherapy, a comprehensive multidisciplinary approach is key for a good outcome. Proper caregiver support should be ensured upfront, and aggressive supportive care should be used. In the setting of an experienced geriatric oncology team, patients with cognitive impairment appear more likely to receive standard oncologic therapies. Cancer patients with cognitive impairment are at high risk of concomitant depression.