To pursue the goal of achieving regular use of mammography in women 40 years of age and older, a risk-based selective approach to screening was implemented at a 400,000-member managed health care system in the Northwest in 1985. This article describes the context for this approach to selective screening and reviews revisions in the algorithm used to determine when and how a woman should be screened. Changes made in 1988 with respect to age criteria, intervals for mammography, and which risk factors to include are discussed. The result of these changes is that 83% of women 40 years of age and older are now eligible for regular mammography compared with 57% under the former system. The total use of mammography in any given year remains unchanged. The results of this analysis have implications for other organizations attempting to promote the use of mammography.