Undertreatment in elderly patients with cancer may be a primary reason for their having poorer outcomes than younger patients. Several studies have shown, however, that otherwise-healthy elderly patients can obtain the same benefits from the same treatment as younger patients. Undertreatment because of age, independent of comorbidities, is apparent in studies of malignancies such as lung, colorectal, and breast carcinomas and lymphoma. The reasons for the bias may include patient preferences, physicians' tendencies to treat patients according to their chronologic age, and a lack of evidence-based guidelines for treating older patients. In many conditions there are few data on the efficacy of treatment in older patients, because of their underrepresentation in randomized controlled trials. Trials of cancer therapy that focus on, or even include, elderly patients should be a priority in the future. Elderly patients are perceived to be less able than younger patients to tolerate standard chemotherapy regimens because of their decreased hematopoietic reserves, the high prevalence of comorbidities, and the greater risk of toxicity. This belief leads to undertreatment through dose reductions and delays that may compromise outcomes. As an alternative, using prophylactic growth factors for hematopoietic support makes it possible for elderly patients to benefit from full doses of the chemotherapy. Establishing age-based standards for cancer care will become more important as the US population ages.