BACKGROUND:Professional organizations have issued guidelines recommending breast cancer screening for women 50 years of age. OBJECTIVE:This study examines the percent of U.S. primary care physicians who report breast cancer screening practices that are not consistent with guidelines, and the characteristics of physicians who reported offering extra test modalities. DESIGN:We analyzed a subset of a 2008 cross-sectional Women's Health Care survey sent to primary care physicians randomly selected from the national American Medical Association (AMA) Physician Masterfile. A subset of physicians received a survey that presented a vignette of a health maintenance visit for an asymptomatic 51-year-old woman who was not at high risk for breast cancer. Responses were weighted to represent physicians nationally. PARTICIPANTS:1,654 U.S. family physicians, general internists, and obstetrician-gynecologists under age 65, who practiced in office or hospital based settings (62.8 % response rate). After exclusions, 553 study physicians remained for analysis. MAIN MEASURE:Physician self-report of breast cancer screening practices that are not consistent with the recommendations of the U.S. Preventive Services Task Force (USPSTF), the American College of Obstetrics and Gynecology (ACOG), and the American Cancer Society (ACS), defined as almost always offering mammography. KEY RESULTS:36.0 % (95 % CI: 31.8 %-40.5 %) of physicians reported offering breast cancer screening tests inconsistent with national guidelines, with most offering extra tests (magnetic resonance imaging [MRI] and/or ultrasound) (33.2 %, 95 % CI 29.1 %-37.6 %). In adjusted analysis, risk-averse physicians and those who believed in the clinical effectiveness of MRI were more likely to offer extra breast cancer screening tests. CONCLUSIONS:Physicians often report offering breast cancer screening test modalities beyond those recommended for a 51-year-old woman. Strategies, such as academic detailing regarding appropriate use of technology and provision of clinical decision support for breast cancer screening, could decrease overuse of resources.