Between 1967 and 1988 128 patients with isolated local-regional recurrence of breast cancer after mastectomy were treated with definitive radiation therapy. Recurrence was confined to a single site in 108 patients and multiple sites in 20. The chest wall was the most common location (86) and the supraclavicular region was the second most common (20). Surgical treatment for recurrence prior to irradiation consisted of excision of all gross disease in 78 patients and incisional biopsy in 49 patients. Irradiation was directed to the entire chest wall in 19% of patients with isolated chest wall recurrences and to the chest wall and regional nodes in 81%. In patients with isolated nodal failures, treatment was directed to the nodal site and chest wall in 87% and to the regional site alone in 13%. Patients with multiple sites received treatment to the chest wall and regional nodes in all cases. Electively treated sites usually received 4500-5000 cGy. Following excision of chest wall disease, the median dose was 6000 cGy. Gross disease on the chest wall received a median dose of 6100 cGy. Gross disease in nodal sites received a median dose of 5600 cGy; 66 patients received systemic therapy at recurrence. The 5-year actuarial local-regional control was 43%. In a multivariate analysis only the estrogen receptor status of the recurrence remained significant (p = .002). The 5-year actuarial survival was 49% with a relapse-free survival of 24%. In a multivariate analysis for survival, the disease-free interval (p = .007), local regional control (p = .006), and excisional biopsy for recurrence (p = .03) remained significant. In a multivariate analysis for relapse-free survival, the disease-free interval (p = .03), excisional biopsy (p = .0001), and the extent of axillary nodal involvement (p = .007) remained significant. In the subgroup of patients with a disease-free interval greater than or equal to 24 months, excisional biopsy, and local regional control, the 5-year survival was 61% with a relapse-free survival of 59%. This subgroup represents 18% of the entire group and has a relatively good prognosis after recurrence.