Two hundred eight cases of intraductal breast carcinoma (DCIS) were selectively treated; 97 with mastectomy, 96 with radiation therapy, and 15 using excisional biopsy only. Mastectomy patients tended to have larger tumors, involved biopsy margins, palpable and often multifocal tumors. Breast preservation patients tended to have smaller, often occult, tumors with clear surgical margins. Before 1983, mastectomy was more common; during and after 1983, breast preservation was more common. Comedocarcinomas were the most frequent tumors. They were the largest, had the highest percentage of microinvasion (20%), and had the highest recurrence rate (8%). Noncomedo DCIS had a recurrence rate of 1%, one of 103 tumors. The recurrence rate for comedocarcinomas treated with radiation therapy was nearly three times higher than for those treated with mastectomy (11% versus 4%). One of 164 (0.6%) axillary lymph node dissections yielded positive nodes. Nine patients have recurred: two in the mastectomy group and seven in the breast conservation group (P less than 0.1). Eight of nine recurrences were the comedo subtype (P less than 0.05). Three patients developed metastatic disease, two of whom have died. Axillary dissection for intraductal carcinoma of the breast is unlikely to yield involved nodes and is not indicated for most cases. It should be reserved for lesions revealing microinvasion. Conservative therapy for comedocarcinoma must be viewed with caution.