The histologic criteria for determining which patients require a reexcision after an initial excisional biopsy for ductal carcinoma in situ (DCIS) of the breast are poorly defined. The authors examined the initial biopsy specimens of 98 patients with inked margins and determined the amount of DCIS on reexcision to help clarify which histologic criteria are useful in judging the need for reexcision. Features in initial biopsy specimens that were associated with an increasing number of slides with DCIS on reexcision were an increasing number of slides with DCIS, an increasing number of DCIS ducts or terminal duct lobular units (TDLUs) with "cancerization" of lobules (COL) within 0.42 cm of the inked margin, and multifocal positive margins. In patients with negative (>0.2 cm) initial biopsy specimen margins, an increasing number of DCIS ducts or TDLUs with COL near the initial biopsy specimen margin were also associated significantly with an increasing number of slides with DCIS on reexcision. Six or more slides with DCIS or 11 or more DCIS ducts or TDLUs with COL within 0.42 cm of the inked margin in the initial biopsy specimens were associated with 6 or more slides with DCIS on reexcision. These results suggest that the amount of DCIS in initial biopsy specimens and the amount of DCIS near the margin are associated with the quantity of DCIS remaining in the breast after an initial excisional biopsy. Pathologists can use these factors when assisting clinicians in evaluating the need for a reexcision.