Alpha-methylacyl coenzyme A racemase (AMACR) is a recently discovered enzyme protein that has been shown to be increased at both the mRNA and protein levels in prostatic adenocarcinoma as compared with normal prostatic tissues. Since its discovery, AMACR has gained wide acceptance for use in the diagnosis of prostatic adenocarcinoma in conjunction with morphology and immunohistochemical staining for basal cell markers. Numerous studies have consistently shown high sensitivity and specificity of AMACR for prostate cancer. This review focuses on AMACR expression in prostate cancer and its morphologic variants, high grade prostatic intraepithelial neoplasia, adenosis and benign conditions of the prostate. In addition, we discuss AMACR expression in other tumors. We also focus on the utility and technical aspects of the now-popular "triple stain" immunohistochemical antibody cocktail, consisting of antibodies to high-molecular-weight keratin, p63 and AMACR. Finally, we emphasize diagnostic pitfalls in the application of AMACR to small, atypical foci of glands seen on prostate needle core biopsy and project future diagnostic as well as clinical applications for the protein.