•Aging can modify the pharmacokinetics and pharmacodynamics of drugs, as well as the tolerance of the tissues.•CGA can help identify those patients with a higher risk of toxicity.•CGA can be used to select drugs and therapeutic schemes that are better tolerated in the elderly.•Predictive scores are less informative than CGA, but they can help in making clinical decisions. Although approximately 50% of cancer patients are 70 years of age or older, cancer treatment in the elderly remains a therapeutic challenge. The elderly form a very heterogeneous group in relation to their general health state, degree of dependence, comorbidities, performance status, physical reserve and geriatric situation, for which therapeutic decisions must be made in an individualized manner. In addition, changes in pharmacokinetics and pharmacodynamics of the drugs occur with age, as well as the tolerance of the tissues, leading to a narrowing of the therapeutic margin and an increase in toxicity. In the general population, Performace Status (PS) has traditionally been used to estimate tolerance to chemotherapy, but in the elderly population it is not useful. In this review we summarize the current knowledge about the pharmacology of antineoplastic drugs in the elderly and the tools available to help us identify risk of chemotherapy toxicity in these patients.