Chemotherapy is associated with transient or permanent cognitive dysfunction ranging from subjective complaints to measurable deficits in working memory, attention and language. Given that old age may be related to cognitive decline, the interaction between chemotherapy-induced cognitive impairment and the effects of age is of growing concern in view of our aging population. Chemotherapy-associated cognitive dysfunction may have an additive impact on pre-existing age-related cognitive performance decline, which calls for awareness in its detection, to reduce impact on quality of life and improve management of older patients. We discuss here the « chemobrain », concept, review the existing evidence about pathophysiology, neuroimaging and cognitive phenotype and propose practical tools for routine detection in the outpatient setting.