Uncontrolled studies suggest that breast conserving therapy can replace radical mastectomy in stage I and stage II breast cancer. Results derived from randomized trials support this conclusion for stage I patients. Although the data are only preliminary, several recent trials also suggest that equivalent results can be obtained in stage II disease. Despite these positive findings, caution should be applied in interpreting the results of both uncontrolled and controlled studies in breast cancer. Issues of concern include variations in the methods of staging disease, short follow-up, failure to report locoregional recurrence rates, and interinstitutional differences in treatment technique and protocol procedures. The introduction of substudies to evaluate the psychosocial and cosmetic results of breast conserving therapy add an important dimension to the overall interpretation of the results.