Sixty percent of all cancer occurs in persons aged > or =65 years. This article provides an overview of aspects of the burden of cancer in the elderly, highlighting certain demographic and epidemiologic data. It served as a frame of reference for participants in the Oncology Geriatric Education Retreat, San Juan, Puerto Rico, February 21-26, 1997. Information comes from several major sources: U. S. Bureau of the Census; National Cancer Institute (NCI) Surveillance, Epidemiology, and End Results (SEER) Program; National Center for Health Statistics; National Institute on Aging (NIA)/NCI SEER Study on Comorbidity and Cancer in the Elderly; and NCI cancer prevalence estimates. Data on the aging population demonstrate an unprecedented expansion of the segment of the population aged > or =65 years. By 2030, 1 in 5 Americans will be aged > or =65 years. Because cancer incidence and mortality rates are highest in persons aged > or =65 years, expansion of this age group takes on great importance for medical professionals who provide treatment to older aged cancer patients. In addition, older aged cancer patients are likely to have preexisting conditions at diagnosis, creating a special clinical challenge. There is an urgent need to better understand the influence of aging on the early detection, diagnosis, and treatment of cancer. Clinicians who treat older persons (geriatricians, oncologists, and other health professionals) can benefit from the integration of the knowledge and approaches of each others' fields. The foundation for this multidisciplinary effort is linked with the education and training of future clinicians.