The authors give the results of the diagnosis and treatment of breast carcinoma in situ (CIS), by studying the data available in the literature and their experience. One hundred and eight patients with CIS were treated. Its detection rate was 1.5%. Non-invasive carcinoma affected the left breast more commonly in 55.6% of cases and the right breast in 44.4%. Their examination established the diagnosis of CIS only in 1.9%. Morphological examination revealed ductal carcinoma in 93 (86.1%) patients, lobular carcinoma in 8 (7.4%), and mixed ductal/lobar carcinoma in 7 (6.5%). Monofocal and multifocal tumor growths were more frequently encountered in ductal carcinoma and multicentric growth was in lobar carcinoma. Axillary lymph node metastases were found in 4.6% patients. Local recurrences were detected in 4 (3.7%) cases. In Group 1, the five-year overall and relapse-free survival rates were 100 and 96.3%, respectively. The characteristic feature of ductal carcinoma is its multifocal growth pattern, i.e. affecting 1-2 ducts within one segment. In lobar carcinoma in situ, multiple tumor rudiments are more common in different parts of the breast. Organ-sparing operations as subtotal resection or subcutaneous mastectomy with one-stage breast reconstruction are adequate for the surgical treatment of patients with noninvasive breast cancer.