Mammograms, specimen radiographs, and pathology reports of 51 women with ductal cancer in situ (DCIS) in 54 breasts were retrospectively analyzed. Reason for presentation was known for 44 women, including six with symptoms due to DCIS and 16 who either had been previously treated for or had (contralateral) breast cancer. Mammographic patterns of DCIS were microcalcifications in 37 of 54 (68%) lesions and calcifications within a mass in 16 (30%). Multifocal DCIS, evidenced radiographically by patterns of more than one mass, more than one cluster of microcalcifications, or parallel linear, irregular intraductal calcifications, was seen in 35 of 54 (65%) breasts but only on specimen radiographs in four of these. In 22 (41%) lesions maximum tumor expanse was greater than 2.5 cm, and all were multicentric. Multicentricity of tumor and tumor size greater than 2.5 cm may indicate need for therapies more radical than simple excision. Breast irradiation has been shown to significantly diminish recurrence rates in these patients. Mammography and specimen radiography with magnification may be appropriate in these cases to identify all possible tumor sites in the involved breast.