The aim of this study was to examine the expression of serotonin receptors in patients with breast cancer and to explore their utility as diagnostic and prognostic markers. Immunohistochemical analysis was performed to examine the expression of serotonin (5-HT) receptor subtypes 1A, 1B, 2B and 4 in a tissue microarray containing tumor specimens from 102 patients. Statistical analysis was performed to correlate the expression of these proteins with regard to clinical parameters. We found that all four serotonin receptors (5-HTRs) exhibited different expression patterns in breast cancer specimens. In general strong staining for 5-HTR1A was observed on the membrane of cancer cells but it was detected only in the cytoplasm of non-malignant cells. 5-HTR1B and 5-HTR2B were predominantly expressed in the cytoplasm of breast cancer cells, while 5-HTR4 was exclusively found in the nucleus of malignant and non-malignant cells. Correlation analysis revealed a significant correlation of 5-HTR2B with estrogen receptor-α (ER-α) and 5-HTR4 with ER-α and progesterone (PR). In conclusion, the different expression patterns and subcellular localization of 5-HTRs in breast cancer may reflect their role in breast cancer progression.