Ductal carcinoma in situ (DCIS) is a heterogeneous disease characterized by noninvasive clonal proliferation of malignant epithelial cells arising from the mammary ducts and terminal ductal-lobular units. Its reported incidence is rising due to the wide adoption of screening mammography. The combination of nuclear grade and presence of necrosis is currently the best predictor of biological behavior. Approximately 25-50% of DCIS lesions progress to invasive disease if left untreated. The treatment options for DCIS include total mastectomy with or without immediate breast reconstruction (IBR), local excision (LE) plus adjuvant radiotherapy (RT), and LE alone. Total mastectomy is associated with lowest rates of local recurrence and breast cancer-specific mortality. If IBR is considered, then skin-sparing mastectomy (SSM) combined with autologous myocutaneous flap reconstruction can achieve excellent cosmesis without compromising local control. The role of adjuvant radiotherapy (RT) after LE remains controversial. Three recent randomized controlled trials have demonstrated that adjuvant RT after LE of localized DCIS significantly reduces the incidence of local recurrence. However, these trials did not identify any subgroups of patients where RT could be safely omitted and were criticized for lack of emphasis on standardized and meticulous tissue processing and pathological evaluation. Retrospective studies indicate that RT can be safely omitted after adequate LE (margin width > or = 1 cm) of small (< 15 mm), non-high grade DCIS not associated with necrosis. The role of tamoxifen in the treatment of DCIS continues to evolve. Formal axillary dissection is not appropriate for DCIS; however, the potential role of the sentinel node biopsy (SNB) in selected high-risk cases requires further evaluation. Areas of ongoing and future research include the potential role of third-generation aromatase inhibitors and third- and fourth-generation selective estrogen receptor modulators in women with hormone-sensitive DCIS; the potential role of cyclo-oxygenase type 2 inhibitors in DCIS treatment and prevention; the value of magnetic resonance and nuclear medicine imaging; and the clinical relevance of gene expression profiling, proteomics, radiofrequency or LASER ablation and mammary ductoscopy in the management of DCIS.