Between 1978 and 1986, 1030 women with clinical Stage I or II breast cancer underwent excisional biopsy, axillary dissection (948 patients), and definitive irradiation. Sixty-five patients developed a recurrence in the treated breast, 9 of which were associated with simultaneous (8) or antecedent (1) distant metastases. Detection was by mammography alone in 29%, physical exam alone in 50%, and both in 21%. The median interval to recurrence was 34 months. Overall, 65% of the recurrences were in the vicinity of the original tumor; however, as the interval to recurrence increased, the percentage of operable recurrences in a separate quadrant increased. For those recurring after 5 years, 54% were in a separate quadrant. Ninety-five percent of the recurrences unassociated with distant metastases were operable and pathology revealed non-invasive cancer only in 10%. Fifty-two patients underwent salvage mastectomy. Thirteen patients had no residual tumor following excisional biopsy at the time of mastectomy. None of the following factors were predictive for no residual tumor: initial age, method of detection, interval to recurrence, location of recurrence, or histology. Local-regional control following mastectomy was 95%. The 5-year actuarial overall and disease-free survivals for salvage mastectomy patients were 84% and 59%, respectively. The only significant prognostic factor for survival was the initial clinical tumor size, which was related to the extent of the recurrence. Based on the inability to identify factors which would predict for a localized recurrence pathologically, we recommend mastectomy as the preferred surgical treatment for an isolated breast recurrence. Adjuvant chemotherapy may be beneficial in patients with an unfavorable prognosis.