The purpose of this study was to determine whether a targeted intervention could improve primary care practitioners' concordance with guidelines regarding management of women with breast symptoms. One hundred and twelve practitioners from randomly selected areas around Australia prospectively audited their investigations for each woman with a new breast symptom over two 12-week periods, before and five months after the release of national guidelines. Between the two audits, doctors received feedback on practice in relation to peers and attended one seminar in their local areas led by specialists from the Royal Australasian College of Physicians and the Royal Australasian College of Surgeons. For five recommendations, there were statistically significant improvements at the second audit in line with standard Investigation of a New Breast Symptom (INBS) guidelines. All these were for investigations of breast lumps. At first audit, there were seven recommendations where practitioners were already managing more than 80% of women in accordance with the INBS, and where there were no statistically significant increases in concordance at second audit. Another six recommendations had lower concordance with the recommendations prior to the release of the guidelines and did not significantly improve at second audit. These tended to be for less-common presentations and where clinical findings were not consistent with other test results. We concluded that a targeted intervention improved physician concordance with current best advice for investigating women who present with new breast symptoms in a primary care setting. Further educational programs are needed to improve investigations for rarer symptoms, and to enhance physicians' confidence in the results of their clinical examinations.