BACKGROUND The purpose of this study was to compare the diagnostic accuracy of fine-needle aspiration (FNA) of clinically suspicious palpable breast masses in women younger and older than 40 years of age. METHODS All women who had FNA biopsy with subsequent tissue biopsy were included. The cytologic diagnoses were classified into three groups: malignant, suspicious, or benign. Histopathologic correlation was based on either a needle core biopsy, an excisional biopsy, or a mastectomy specimen. RESULTS A total of 1,158 fine-needle aspirations performed between 1982 and 2000, on women being evaluated for a clinically palpable breast mass were included in the study. The patients were divided into two groups: group I consisted of 231 patients aged 40 years and younger, and group II consisted of 927 patients aged 41 years and older. In group I there were 117 (51%) malignant FNA diagnoses, and only 1 (1%) false-positive case, subsequently diagnosed on histopathologic material as an atypical papillomatosis. There were 20 (9%) cases diagnosed as suspicious on FNA. On histopathology 10 were malignant, and 10 were benign. Of the 91 (39%) cases interpreted as benign, only 1 (1%) was a false negative. In group II, which comprised 927 patients, there were 693 (74%) malignant FNA diagnoses, and 3 (less than 1%) false-positive cases, which on follow-up histopathologic examination revealed 2 atypical ductal hyperplasias and 1 atypical papilloma. There were 90 (10%) cases diagnosed as suspicious on FNA. On histopathology, 68 were malignant and 22 were benign. Of the 131 (14%) lesions interpreted as benign, there were 18 false-negative cases (14%), which included 17 infiltrating carcinomas and 1 ductal carcinoma in-situ. Twelve (1%) of the cases were inadequate for the study. CONCLUSIONS The sensitivity, specificity, and positive predictive values were remarkably high and comparable in both groups: group I had 99% sensitivity, 99% positive predictive value, 99% specificity, and 99% negative predictive value; and group II had 98% sensitivity, 97% specificity, 99% positive predictive value, and 86% negative predictive value. The overall rate of false-positive (less than 1%) and false-negative cases (9%) is comparable with published literature. Suspicious cases should be further evaluated, as our study revealed more than 50% to be malignant. The incidence of malignancy in patients presenting with a clinically palpable breast mass with follow-up biopsy was 51% in patients aged 40 years and younger and 74% in patients aged 41 years and older. Fine-needle aspiration is an excellent diagnostic tool in assessing clinically palpable breast masses.