Failure to diagnose breast carcinoma by fine-needle aspiration (FNA) is a major obstacle to expanded use of that technique. While the majority of false negative diagnoses are due to inadequate sampling and insufficient specimens, a significant minority of false negative cases result from inaccurate interpretation of adequate material. Low grade carcinomas including lobular, tubular, low grade adenosquamous, and papillary carcinomas appear to account for many of these diagnostic errors. Careful attention to nuclear detail, monomorphism of cell population and the presence of neoplastic cells with retained cytoplasm should allow the recognition of the majority of these neoplasms as malignant by cytologic examination.