The benefits and risks of breast cancer screening via mammography have been the subject of controversy recently. In this article, we review these benefits and risks. Randomized trials show a 21% reduction in breast cancer mortality following screening invitations. The plausible effect of participation in screening is even greater. Most observational studies of organized screening programs yield similar or slightly more favorable results. Estimates of screening-induced overdiagnosis vary widely across studies, primarily because some do not fully account for effects such as earlier diagnosis and changes in the underlying incidence of breast cancer. Studies that account for these effects estimate overdiagnosis rates of around 10% or less. The benefits of mammography screening outweigh the risks. (R.A.)