The optimal local-regional treatment for patients with Stage III breast cancer has not been determined. To evaluate the effectiveness of radiation therapy as local treatment for such patients, the results of 192 patients (five with bilateral disease) treated with radiation therapy without mastectomy between July 1, 1968 and December 31, 1981 were reviewed. Excisional biopsy (gross tumor removal) was performed in only 54 of the 197 breasts. Patients typically received 4500 to 5000 cGy in 5 weeks to the breast and draining lymph nodes; a local boost to areas of gross disease was delivered to 157 patients. Multi-agent chemotherapy was given to 53 patients. The median follow-up was 65 months. The actuarial probability of survival for the entire group was 41% at 5 years and 23% at 10 years. The probability of relapse-free survival (RFS) was 30% at 5 years and 19% at 10 years. The addition of multi-agent chemotherapy was associated with a significantly improved 5-year RFS (40% versus 26%, P = 0.02). The 5-year survival rate was 51% for patients who received adjuvant multi-agent chemotherapy and 38% for patients who did not (P = 0.16). The actuarial rate of local-regional tumor control (not censored for distant failure) for all patients was 73% at 5 years and 68% at ten years, and the crude incidence of local-regional control was 78%. Local-regional tumor control was principally influenced by radiation dose. Patients who received 6000 cGy or greater to the primary site had a better 5-year rate of control in the breast than did patients who received less than 6000 cGy (83% versus 70%, P = 0.06). Significant complications were seen in 15 patients (8%); these included moderate or severe arm edema in six patients and brachial plexopathy in four patients. Cosmetic results at last evaluation were excellent or good in 56% of evaluable patients, fair in 25%, and poor in 19%. It is concluded that high-dose radiation therapy without mastectomy is an effective means of controlling local-regional tumor in patients with locally advanced breast cancer.