On May 1, 1997, the American Cancer Society (ACS) published its recommended mammography screening interval for women ages 40-49 years from once every 1 to 2 years to once every year. At the same time, the National Cancer Institute (NCI), which had previously not recommended routine screening of women in their 40s, began recommending screening at 1 to 2-year intervals.

These events occurred during the data collection phase of a prospective study of mammography screening and, thereby, provided an unexpected opportunity to examine the potential influences of changing guidelines on women’s beliefs about how frequently they should obtain screening exams.

The recommendations were based on information from an ACS sponsored workshop convened in March 1997 to consider new scientific findings related to breast cancer screening and to determine whether these findings warrant a change in the existing ACS guidelines. The meeting was timed so that participants could benefit from new data related to screening women aged 40 to 49 years. A recommendation based on the new data and subsequently approved by the ACS Board of Directors is reported.