Few series are published on DCIS that forms parenchymal lesions on screening mammograms. The implications of these unusual presentations for pre-operative assessment and surgical intervention are of interest. In the setting of a large, population-based breast cancer screening program, the diagnostic and management implications of DCIS presenting as parenchymal lesions on screening mammograms are investigated. A total of 125 lesions (20.1% of all DCIS) presented as a mass (n=99) or microcalcifications with an associated parenchymal lesion (n=26). Cytology was positive in 47.1% of cases. Core biopsy diagnosed DCIS in 68.4% of cases. Breast surgery after a definite preoperative diagnosis achieved negative initial margins in 69.4% case, versus 54.7% without a pre-operative malignant diagnosis. The mastectomy rate was 26.4%. Axillary surgery was carried out in 32.8% cases, including axillary clearance in 26.4% of cases. One in five cases of DCIS detected during mammographic screening has features other than pure microcalcifications. This has implications for pre-operative assessment and surgical management.