The incidence of intraductal carcinomas (IDC) of the breast is increasing. However, few cases have been reported in young women. Based on a series of 13,168 women treated for breast cancer at the Institut Curie over a 12-year period, this article analyses the prevalence, clinical presentation, prognosis and treatment of IDC in patients younger than 35 years. Of this series of 13,168 cancers, 882 occurred in women under the age of 35 years (6.7%). Sixteen of these cases (2%) were strictly intraductal lesions and therefore constituted the study population. The frequency of IDC in women under the age of 35 years was identical to that of IDC in the general population of this study. The circumstances of discovery were: palpable tumour in seven cases (44%), mammographic discovery in four cases (25%), nipple discharge in five cases (31%). Histological examination revealed a well-differentiated IDC in two cases, moderately differentiated in seven cases and poorly differentiated in five cases (two cases not specified). Conservative treatment by lumpectomy and irradiation was performed in nine patients, and another seven patients were treated by mastectomy and low axillary lymph node dissection. The mean follow-up was 83 months (range: 5 to 156 months). A single patient has relapsed: an isolated invasive mammary recurrence, 6 years after conservative treatment. This patient in now in complete remission after mastectomy. All patients are therefore alive, with no evidence of disease, at 83 months. In the group of women younger than 35, the frequency of IDC appeared to be identical to that observed in the general population. Their prognosis after treatment is excellent, and identical to that of IDC in older women. Conservative treatment is justified in localized forms, but mastectomy with immediate reconstruction must be performed in the presence of extensive disease.