Seventy-six patients with intraductal carcinoma (DCIS) of the breast have been observed for 83 months (range 50-141) following treatment by lumpectomy (L) only (21), L and breast irradiation (XRT) (27), or mastectomy (28). All represented examples of DCIS retrieved after pathologic examination of a much larger cohort of patients with stage I and II invasive breast cancer enrolled in NSABP protocol 6. Local breast recurrences were similar for women with DCIS and those from this cohort at a similar period of follow-up with invasive cancer treated by L only (43% vs. 39%) and L + XRT (7% vs. 10%). The presence of moderate/marked comedonecrosis was suggestively related to local breast recurrence (P = .07). This latter was significantly reduced for patients receiving post L XRT (P = .01). All local breast recurrences in this study and 29 of 31 recorded by others occurred at or close to the site of extirpation of the index cancer minimizing multicentricity as a contraindication for the conservative surgical treatment of DCIS. Survival rates which were similar for patients with DCIS regardless of form of local treatment were better than that observed for negative node patients with invasive cancer enrolled in protocol 6. Thus, DCIS is a less, not more, ominous disease than invasive cancer. This and other features of its natural history indicate that it would be a contradiction to treat invasive cancer but not DCIS conservatively.