The clinical, cytopathologic and histopathologic features of a case of gynecomastia induced by chemotherapeutic drugs are described. Fine needle aspiration (FNA) smears showed epithelial atypia, and an erroneous cytologic diagnosis of carcinoma was made. Histopathologic study showed gynecomastia with epitheliosis, papillomatosis and atypical ductal hyperplasia. Review of the FNA smears showed the findings to be more typical of a reparative or regenerative process; these findings had been cytologically overinterpreted, partly due to the lack of adequate clinical information submitted with the aspirate. The possible causes of gynecomastia, the induction of epithelial atypia by cytotoxic chemotherapy and the cytologic features whose recognition may prevent false-positive diagnoses in such cases are discussed.