PURPOSE: There are few data on the effects of disease biology and competing mortality on the effectiveness of screening women for breast cancer after age 65 years. The authors performed a review to determine the costs and benefits of mammography screening after age 65 years. DATA SOURCES: Cost-effectiveness articles published between January 1989 and March 2002. STUDY SELECTION: Studies were identified by using MEDLINE and the National Health Service Economic Evaluation Database. The authors included research on screening after age 65 years conducted from a societal or government perspective; reviews and analyses of other technologies were excluded. DATA SYNTHESIS: 115 studies were identified and 10 met inclusion criteria. One study modeled age-dependent assumptions of disease biology. No study fully captured the potential harms of screening, including anxiety associated with false-positive results, overdiagnosis, and previous knowledge of cancer or living longer with the consequences of treatment. Studies differed in the specific strategies compared and in analytic approaches. On average, extending biennial screening to age 75 or 80 years was estimated to cost 34 000 dollars to 88 000 dollars (2002 U.S. dollars) per life-year gained, compared with stopping screening at age 65 years. Two studies suggested that it was more cost-effective to target healthy women than those with several competing risks for death. CONCLUSIONS: Current estimates suggest that biennial breast cancer screening after age 65 years reduces mortality at reasonable costs for women without clinically significant comorbid conditions. More data are needed on disease biology and preferences for benefits and harms in older women.