OBJECTIVE To determine an effective, evidence-based postoperative surveillance strategy for the detection and treatment of recurrent breast cancer. Tests are recommended only if they have an impact on the outcomes specified by the American Society of Clinical Oncology (ASCO) for clinical practice guidelines. POTENTIAL INTERVENTION: All tests described in the literature for postoperative monitoring were considered. In addition, the data were critically evaluated to determine the optimal frequency of monitoring. OUTCOME Outcomes of interest include overall and disease-free survival, quality of life, toxicity reduction, and secondarily cost-effectiveness. EVIDENCE A search was performed to determine all relevant articles published over the past 20 years on the efficacy of surveillance testing for breast cancer recurrence. These publications comprised both retrospective and prospective studies. VALUES Levels of evidence and guideline grades were rated by a standard process. More weight was given to studies that tested a hypothesis that directly related testing to one of the primary outcomes in a randomized design. BENEFITS/HARMS/COSTS: The possible consequences of false-positive and negative tests were considered in evaluating a preference for one of two tests that provided similar information. Cost alone was not a determining factor. RECOMMENDATIONS The attached guidelines summarize the recommendations of the ASCO breast cancer expert panel (see Table 1 for a summary of guidelines and corresponding levels of evidence and grades of recommendation). Data are sufficient to recommend monthly breast self-examination, annual mammography of the preserved and contralateral breast, and a careful history and physical examination every 3 to 6 months for 3 years, then every 6 to 12 months for 2 years, then annually. Data are not sufficient to recommend routine bone scans, chest radiographs, hematologic blood counts, tumor markers (CEA, CA15-5), liver ultrasonograms, or computed axial tomographic scans. VALIDATION The recommendations of the breast cancer expert panel were evaluated by the ASCO Health Services Research Committee reviewers and by the ASCO Board of Directors.