Ductal carcinoma in situ (DCIS) is a pre-invasive stage of breast cancer with a heterogeneous clinical behaviour. Since the introduction of mammographic screening programmes, the incidence of DCIS has shown a dramatic increase. Treatment should focus on the prevention of progression to invasive disease. If progression occurs, poorly differentiated DCIS frequently gives rise to grade III invasive breast cancer, whereas well differentiated DCIS more often recurs as grade I invasive disease. However, at present, validated diagnostic test are lacking to predict progression accurately. The majority of women with DCIS are suitable for breast conserving therapy. Obtaining clear surgical margins is the most important goal of a local excision. Radiotherapy is effective in reducing the risk of local recurrence with about 50 % in all subgroups of patients with DCIS. (Breast cancer specific) survival of women with DCIS is excellent, and radiotherapy does not further improve this. Future research should be directed in enabling to select women who have a high risk of--invasive--recurrence, so in which radiotherapy should be standard part of the breast conserving approach, and those women with a more indolent lesion, in which after surgery a watchful waiting approach can be followed.