Results of radiation therapy following breast-conserving surgery were analyzed for 410 patients with clinical Stage I-II mammary carcinoma having a minimum and median follow-up time of 5 years and 11 years, respectively. Crude survival rates were 82.2% at 5 years, 62.5% at 10 years, and 45.4% at 15 years. Local-regional recurrence was observed in 9.7% of patients. Seventy-five percent of these recurrences could be controlled locally by further treatment. Both local recurrences and metastatic deaths were more frequent in patients in clinical Stage II and in patients 40 years of age or younger. The cosmetic result was judged good to excellent in 77% of patients, with unacceptable results in 6.7%. The majority of poor results were seen in patients receiving 60 Gy or more to the entire breast. Arm edema occurred in 25% of patients having had axillary dissection, and in 3.4% of patients without axillary surgery. Edema was confined mainly to patients having had axillary doses of 60 Gy or more, and was never disabling. This study demonstrates that excellent long-term results are obtainable with breast-conserving techniques in early breast cancer. Satisfactory cosmetic results and a very low complication rate can be expected if extensive axillary surgery is avoided in conjunction with axillary radiation, and if the radiation dose applied to large treatment volumes is restricted to 50 Gy.