Benign and malignant papillary neoplasms of the breast may be difficult to distinguish in both cytologic and histologic preparations. To define the cytologic features of benign and malignant papillary lesions, we retrospectively reviewed 18 cases of fine needle aspirates from histologically confirmed cases of papilloma or papillary carcinoma of the breast. This study included 3 intraductal papillary carcinomas, 3 invasive papillary carcinomas, and 12 intraductal papillomas. Ail cases were evaluated for presence or absence of papillary fragments, bloody background, apocrine metaplasia, macrophages, and degree of cellularity, atypia, and single isolated columnar epithelial cells. Papillary fragments were present in all cases. The background of the smear was bloody in all 6 carcinomas, but in only 7 out of 12 papillomas. Markedly increased cellularity was present in 4 carcinomas(67%) and 7 papillomas(58%). Single cells were present in 5 carcinomas(83%) and 8 papillomas(67%). The majority of papillomas and papillary carcinomas had mild to moderate atypia, and severe atypia was noted in one case of intraductal papillary carcinoma and one case of invasive papillary carcinoma. Apocrine metaplasia was absent in all cases of papillary carcinomas, but present in 8 papillomas(57%). Macrophages were noted in 4 carcinomas and were present in all cases of papillomas. The constellation of severe atypia, bloody background, absence of apocrine metaplasia and/or macrophages were features to favor carcinoma. Malignant lesions tended to show higher cellularity and more single isolated cells. The cytologic features mentioned above would be helpful to distinguish benign from malignant papillary lesions of the breast. However, because of overlapping of cytologic features, surgical excision should be warranted in all cases on papillary lesions of the breast to further characterize the tumor.