Between 1967 and 1977, 36 patients received treatment at the Virginia Mason Medical Center in Seattle, Wash, for ductal carcinoma in situ of the breast. Twenty-five patients had modified radical mastectomies, 10 had radical mastectomies, and one had a simple mastectomy. Twenty-seven patients have been followed up for at least 10 years and are without known recurrence (mean follow-up, 17.7 years; range, 8 to 24 years), eight patients died without known recurrence (mean follow-up, 10.6 years; range, 6 to 14 years), and one patient with a prior contralateral mastectomy for infiltrating cancer of the breast had a recurrence in the scalene nodes on the side of the infiltrating cancer and died of metastatic cancer. No patients with ductal carcinoma in situ had local recurrences in the ipsilateral breast or chest wall, and no patients developed cancers in the contralateral breast; one patient had axillary metastasis. Twenty-eight (78%) of 36 patients had multicentric ductal carcinoma in situ in their mastectomy specimens. Twenty-three (88%) of 26 patients with comedocarcinoma-type ductal carcinoma in situ had multicentric lesions. Conversely, patients with low-grade nuclear papillary ductal carcinoma in situ did not have multicentric lesions. Five (14%) of 36 patients had incidental microinvasion discovered in the mastectomy specimens; all had comedocarcinoma. In summary, our study of patients with ductal carcinoma in situ revealed that (1) mastectomy provided excellent local and systemic control; (2) cancer in the contralateral breast was infrequent; (3) axillary metastasis was rare; and (4) histologic features of tumors markedly affected the frequency of multicentricity and chance for microinvasion.