While researchers have established the value of screening for breast cancer with mammography, with and without clinical breast examination, age-specific analyses have led to differing opinions regarding the ages and the intervals that breast cancer screening should begin. This article, therefore, provides a detailed, age-specific evaluation of mammography screening by assessing the severity of breast cancer, the effectiveness of earlier versus later treatment, and the accuracy and reliability of mammography. Data from previous randomized trials and other sources are used to evaluate these criteria. The results indicate that screening programs must have high levels of participation, achieve acceptable sensitivity (85%) and specificity (90%), adopt age-specific screening intervals, and consider how disease stage influences diagnosis. In addition, as others have noted, the following benchmarks can be used to evaluate screening programs: (1) more than 50% of screen-detected cancers should be smaller than 15 mm; (2) 30% or more of grade 3 cancers detected on screening should be less than 15 mm; and (3) more than 70% of cancers detected on screening should be node negative.