Complete excision is key to successful breast-conserving treatment for patients diagnosed with ductal carcinoma in situ (DCIS). Patients with extensive DCIS should be considered the choice of mastectomy (followed by reconstruction), while for smaller DCIS breast-conserving treatment should be performed by complete excision. This review reports on the effect of margins on the clinical management of patients with a diagnosis of DCIS. The role of preoperative imaging including MRI, surgical procedures, and pathology are described. J. Surg. Oncol. 2008;98:579–584. © 2008 Wiley-Liss, Inc.