Morphologic analysis of nuclear grade and extent of necrosis can provide reproducible classification of subclinical duct carcinoma in situ (DCIS) which strongly separates DCIS into three risk groups. For subclinical lesions of small size, risk is largely limited to local recurrences only, half of which, however, are invasive events. Local recurrences are seen much more frequently with high grade DCIS. Most local recurrences following breast conservation therapy represent residual disease in the immediate vicinity of the biopsy site. Stromal and cellular host reactions may provide additional prognostic information.