Cancer in older patients is an international health problem of mounting importance, resulting from the slow rise in the proportion of the population over 65. Age is the major risk factor for malignancy, with two-thirds of cancer deaths in the USA in those over 65. By 2000 this will be the same in Europe. Most treatment trials have included only patients under 65 and results cannot necessarily be applied to older patients. Many trials now include older patients, but these may overestimate population benefits by excluding the particularly frail.