A number of studies have shown the value of fine needle aspiration cytology for the diagnosis of breast lesions, but reports on the comparison of cytologic and histologic variations of breast cancers are few. We reviewed histologically proven 106 breast aspirates with an emphasis on the cytology of ductal carcinomas and of an area of uncertain atypia. Positive and negative predictive values of breast aspiration cytology were 100% On review of the cases originally diagnosed as atypia of uncertain nature (19 %), features more suggestive of malignancy or benignancy were recognizable in most underdiagnosed cases and a half of overdiagnosed cases, respectively. However, indistinguishable atypism also remained. Thirty seven cases out of 53 infiltrating duct carcinomas revealed malignant cytology, with variations in background, cellularity, morphology of cell groups, and extent of isolated tumor cells. When classifying the infiltrating duct carcinomas into scirrhous, solid-tubular, and papillotubular types, scirrhous type frequently appeared as irregularly shaped tight or loose cell clusters, and solid-tubular type as round-margined cell balls.