Between 1982 and 1985, 108 women with AJC Stage I and II invasive mammary carcinoma were treated to 115 breasts with conservative surgery and irradiation. The irradiation dose was adjusted to the histopathological normal tissue margin around the carcinoma in the tumor excision specimens. Margins were arbitrarily determined negative, close, and positive with normal tissue margins in the inked tumor excision specimens of greater than 5 mm, 2-5 mm, and less than 2 mm, respectively. Negative, close, and positive tumor margin patients were treated to radiation doses of 60, 65, and 70 Gy, respectively. The boost in excess of 50 Gy was directed to the tumor bearing quadrant of the breast using interstitial Ir-192 implants for doses greater than or equal to 70 Gy. The draining lymphatics were irradiated to 50 Gy except in patients with tumor in the lateral half of the breast and no axillary lymph node metastases. Histopathological evaluation of re-excision specimens revealed the difficulty of obtaining negative margins for tumors greater than 2 cm. By our criteria, 54% of the patients had a positive resection margin. None of the patients experienced a local recurrence at 60 months median follow-up. Three patients failed regionally, two in un-irradiated lymph node areas, one in the skin of the contralateral breast; five patients failed systemically. Overall and disease-free survival for Stages T1/N0, T1/N1, T2/N0 was 100 and 95%, respectively, and for T2/N1, 90 and 80%, respectively. The cosmesis was excellent in 66% of the patients with minimal treatment related complications. Carefully planned standardized irradiation with assessment of resection margins yields both excellent local control rates and cosmetic results.