Ductal carcinoma in situ (DCIS) is a non-invasive breast carcinoma that remains in the milk ducts. It is a poorly understood disease and its natural history is not well known. This is because once diagnosed, DCIS is usually treated. It is known however that ductal carcinoma is a precursor of invasive breast carcinoma, as 14-53% can become invasive over a period of 10 years, if left untreated. With increasing knowledge about the molecular biology of DCIS, more insight is given in its relation to invasive breast cancer. Diagnosis of ductal carcinoma in situ is increasing in the last few years. This is likely caused by the increased mammographic screening for breast cancer and the higher quality of mammographic images. DCIS represents about one fifth of all mammographically detected breast cancers. Risk factors for the development of ductal carcinoma in situ are: low parity, late age at first birth and menopause, and Body Mass Index. The Van Nuys Prognostic Index is a useful scoring system to grade DCIS. DCIS is graded by scoring four characteristics: patient's age, margin width, tumor size and pathological classification. It allows us to divide DCIS lesions into different groups according to risk of local recurrence: low risk, intermediate risk and high risk. Each group requires a different treatment, respectively: local excision of the tumor; local excision and radiotherapy; and mastectomy. The use of tamoxifen in the treatment of DCIS is still controversial, but research so far has encouraging results. Interesting developments have been made in the use of Her-2 pulsed dendritic cell vaccination before DCIS surgery.