The purpose of the study was to compare the accuracy of FNAC, CNB, and combined biopsy according to tumor size of suspicious breast lesions.FNAC and CNB were performed in 264 patients with suspicious breast lesions from August, 1997 to August, 2002. The procedures were guided by ultrasound and performed in the same session by the same operator. The lesions were divided in four groups according to the tumor size in the histopathology report: lesions smaller than 1 cm, between 1 and 2 cm, between 2 and 5 cm, and lesions greater than 5 cm.The final surgical histopatology results identified 222 (84%) malignant cases and benign lesions summed 42 (16%). For lesions smaller than 1 cm, FNAC, CNB, and combined biopsy were equivalent for all parameters. For lesions between 1 and 2 cm, FNAC and CNB were equivalent. Combined biopsy showed higher absolute sensitivity (P ¼ 0.007) and lower inadequate rate (P ¼ 0.03) when compared to FNAC. However, when combined biopsy and CNB were compared, no difference were found. For lesions between 2 and 5 cm, CNB showed higher absolute sensitivity (P < 0.001) and lower inadequate rate (P < 0.007) when compared to FNAC. Combined biopsy showed higher sensitivity compared to FNAC and CNB alone (P < 0.05) in this group. For lesions greater than 5 cm, FNAC and CNB were equivalent for all parameters. Combined biopsy only showed higher absolute sensitivity (P ¼ 0.04) when compared with FNAC alone.The combination of FNAC and CNB can improve the diagnosis of suspicious breast lesions higher than 1 cm. However, for lesions smaller than 1 cm, our results showed no difference between FNAC, CNB, and combined biopsy, for these lesions any modality has technical limitations. Diagn. Cytopathol. Key Words: breast cancer; tumor size; fine-needle aspiration cytology; core biopsyThe role of fine-needle aspiration cytology (FNAC) and core needle biopsy (CNB) in establishing the diagnosis of breast disease has been clearly demonstrated. Several studies have compared FNAC and CNB 1-5 with heterogeneous results. It is difficult to decide from published studies which method is preferred. Results may be influenced by patient selection, incidence of breast carcinoma in the population, availability of follow-up data, duration of follow-up, differences in biopsy technique, operator expertise, and interpretation of the results.6,7 Many published series are from academic centers and not from a general hospital setting. Calculations for accuracy are made in different ways sometimes reflecting the clinical effectiveness of the procedure, sometimes only evaluating the laboratory performance. Comparisons between series can only be made after recalculation. 7This study compares the results of FNAC and CNB according to the tumor size taken from the same lesion by the same operator in one session under ultrasound guidance. Materials and MethodsFNAC and CNB were performed in 264 patients with suspicious breast lesions from