Fine needle aspiration (FNA) has been proven to be accurate for the detection of breast carcinomas. However, its utility in the classification of benign breast lesions is less clear. We therefore undertook a study of 76 adequate preoperative FNAs of the breast from patients whose surgical biopsies of the breast were shown to be benign (18 nonproliferative diseases, 30 fibroadenomas, 19 proliferative breast diseases without atypia, and 9 proliferative breast diseases with atypia). A number of architectural and cellular features on cytology were evaluated. Histology slides were also reviewed. Both cytology and histology specimens were categorized as nonproliferative disease, fibroadenoma, proliferative breast disease without atypia, and proliferative breast disease with atypia. There was exact diagnostic correlation between cytology and histology in only 42 (55%) of the 76 cases. No cellular or architectural features on FNA examined correlated with the presence of epithelial proliferation on histology. The presence of two epithelial cell populations (one unremarkable and one atypical), small but prominent nucleoli, and nuclear pleomorphism on FNA significantly correlated with the presence of atypia on histology. However, these features are also present in breast lesions without proliferation or atypia, and are not diagnostic of atypical proliferative lesions of the breast. Therefore, FNA of the breast is limited in classifying benign breast diseases.