Abstract: Objective To retrospectively analyze the false-negative rate of ultrasonography(US)-guided core-needle breast biopsy(CNB) in BI-RADS 4b-4c lesions through comparison with surgical excision histologic examination and assess the early and late complications. Methods One hundred and seventy patients with 173 breast lesions classified BIRADS 4b and 4c by ultrasound were performed 14-gauge core needle biopsy guided by US using local aneathsesia.All patients underwent surgical excision，including modified radical mastectomy，breast conserving surgery for invasive breast cancer or lumpectomy for benign lesions，according to the pathological results from core needle biopsy.Using the pathological results from the surgical excision samples as golden standard.The complications during preoperative period and long term complications were collected retrospectively and recorded. Results US guided 14-gauge CNB yielded 141(81.5%) malignant，and 32(18.5%) benign lesions including fibroadenoma(26 lesions) and other benign lessions(6 lesions).In 3 patients with bilateral lesions,1 case of bilateral breast cancer and 2 cases were one side and the other side fibroadenoma.False-negative finding was encountered in 1 of 170 cases，and the false-negative rate was 0.7%(1 of 141 malignancies).The sensitivity and specificity of the core needle biopsy histology diagnosis were 99.3% and 100% compared with the surgery pathological results.The negative predictive value(NPV) was 96.8%.The incidence of hematoma was 2 case.There were 45 cases with the local ecchymosis.There were no core needle biopsy associated infection,implantation metastasis or local recurrence during median 32 months follow-up. Conclusion Ultrasonography(US)-guided 14-gauge core-needle breast biopsy(CNB) is an effective and safe method for breast cancer diagnosis.