The elevated expression of P504S gene and its product alpha-methylacyl-CoA racemase (AMACR) can serve as a molecular marker for prostate cancer. The goal of this study is to investigate P504S/AMACR expression in fine-needle aspiration smears and correlate it with cytological diagnosis. Immunocytochemistry was performed in 35 patients with morphological diagnosis of prostate carcinoma (n = 16), atypia (n = 15), and benign hyperplasia (n = 4). Among 16 malignant cases there were two low-grade, eight intermediate, and six high-grade prostate carcinomas. Cytoplasmic positivity is analyzed qualitatively as predominantly diffuse or focal and quantitatively as <5%, 5-50%, and >50% of cells. Benign cases showed no P504S/AMACR expression. Positive staining was recorded in 75% of malignant cases, but in the majority of them it was weak and focal or diffuse and in a small amount of cells. The most intensive staining was seen in low-grade carcinomas and some atypical cases. This observation indicates a correlation between P504S/AMACR expression and differentiation of cells. P504S/AMACR staining might be of great value in cytodiagnosis of prostate lesions as well as an example of the characterization of cells at the molecular level using fresh tissue obtained by fine-needle aspiration.