Core-needle biopsy (CNB) of breast lesions can be classified into 5 categories according to lesion type and associated risk of malignancy. B3 category (lesion of uncertain malignant potential) constitutes a challenging problem in clinical decision, with most ending in excisional biopsy. Therefore, the aim of this study was to establish the incidence of malignancy on excision biopsy of B3 lesions and assess if subclassification (in B3a and B3b categories) according to the presence of atypia in otherwise B3 lesions better predicts malignancy on excision. Forty-eight cases with diagnosis of B3 lesion on CNB and matched surgical excision specimen were included to evaluate the positive predictive value (PPV) and odds for malignancy in CNB. All cases were further subclassified into B3a and B3b categories. B3 category lesions had an overall PPV for malignancy of 12.5% and significant low odds of malignancy of 0.14. When subclassified, B3b (lesions with atypia) demonstrated a higher PPV for malignancy (36.36%) with a nonsignificant odds. Inversely, B3a (lesions without atypia) demonstrated a PPV for malignancy of only 5.41% and a significant low odds of malignancy of only 0.06. The described low rate of malignancy in some of B3 lesions additionally reinforces the practice of avoiding surgical excision in selected patients and provides data that additionally support B3 lesion subclassification according to the presence of atypia. Subclassification of B3 category can further refine the current classification of associated risk of malignancy with possible implications in clinical management.