Atypical ductal hyperplasia (ADH) diagnosed by core needle biopsy (CNB) is regarded as an indication for surgical excision. We investigated whether histologic subtype and extent of ADH in a series of 123 CNB specimens can predict the presence of carcinoma on surgical excision. We found that ADH present in more than 2 foci in CNB specimens was a strong predictor of ductal carcinoma in situ (DCIS) on excision (>2 foci, 16/41 vs 6/82 for 1 or 2 foci; P < .0001). The micropapillary subtype of ADH also predicted the presence of DCIS (P = .0006). Our study suggests that micropapillary histologic subtype and extent of ADH in CNB specimens can be applied to predict the presence of DCIS on surgical excision. By using the combination of the extent of ADH in CNB specimens (1 or 2 foci), the presence of microcalcifications within the lesion, and the lack of residual mammographic calcifications after CNB, we identified a low-risk group of patients (n = 25), none of whom had carcinoma on surgical excision. Patients with ADH restricted to fewer than 3 foci may not need surgical excision, especially when the mammographic abnormality is completely removed by CNB.