Mammary recurrences were studied in 1593 patients with Stage I and II breast cancer treated by macroscopically complete tumor excision followed by megavoltage radiotherapy, including a boost to the tumor bed (mean dose, 78 Gy). The actuarial freedom from mammary recurrence was 93% at 5, 86% at 10, 82% at 15, and 80% at 20 years. Seventy-nine percent of the recurrences were in the vicinity of the tumor bed, but with increasing time interval, an increasing percentage of recurrences was located elsewhere in the breast. A majority of recurrences after 10 years could be considered new tumors. Only ten of 181 patients with recurrence had prior or concomitant distant metastases, and 159 of 171 isolated mammary recurrences (93%) were operable. Uncorrected overall survival after operable recurrence was 69% at 5 and 57% at 10 years. Prognosis after late recurrence (after 5 years) was favorable (84% 5-year survival). Operable early recurrences retained a favorable prognosis if smaller than 2 cm and confined to the breast (74% 5-year survival). Disease-free interval and histologic grade also appeared to be important prognostic factors after early recurrence. Survival after recurrence did not depend upon the type of salvage operation. Locoregional control was 88% at 5 years after salvage mastectomy and 64% after breast-conserving salvage procedures. The role of adjuvant systemic therapy at time of local recurrence requires additional study. This experience illustrates the important differences between mammary failure and chest wall recurrence after mastectomy, in particular the protracted time course and more favorable prognosis associated with the former.