Although fine-needle aspiration cytology is a routine procedure for the diagnosis of breast carcinoma, cytologic specimens have rarely been used for evaluation of hormone receptor status and HER2/neu overexpression. In order to compare the biological markers on cytology and on histology, routinely fixed smears of 110 primary breast carcinomas were immunostained for estrogen receptor (ER), progesterone receptor (PgR), and HER2/neu by automated immunostainer and the results were compared with the corresponding histologic sections. ER was expressed in 76 of 110 (69%) cases and PgR was expressed in 51 of 110 (46%). Overexpression of HER2/neu was observed in 30 of 110 (27%) cases. Concordance between cytology and histology was 98% for ER, 95% for PgR, and 100% for HER2/neu. There was no false positive result on smears. Diagnostic pitfalls in determination of hormone receptor status on smears included intratumoral heterogeneity and presence of mucin. Diagn. Cytopathol. 2004;30:251–256. © 2004 Wiley-Liss, Inc.