The aim of this review was to determine the effectiveness of screening mammography in women aged 40 to 49 years at average risk for breast cancer. The following questions were asked: Does screening mammography for women aged 40 to 49 years who are at average risk for breast cancer reduce breast cancer mortality? What is the sensitivity and specificity of mammography for this age group? What are the risks associated with annual screening from ages 40 to 49? What are the risks associated with false positive and false negative mammography results? What are the economic considerations if evidence for effectiveness is established?