Prostate secretory protein of 94 amino acids (PSP94), primarily found in the prostatic secretion, was originally isolated and purified from human seminal plasma. PSP94 has several putative biological functions and is considered a marker of prostate cancer (PCa). Here, we review the structural-functional relationships of PSP94, address its fungicidal activity and role as an inhibitor of sperm motility and protection from female immune surveillance, and review its role in tumor suppression. We also review the diagnostic assays that are developed for PSP94 for use in the diagnosis of PCa and use of such tests in the differential diagnosis of PCa from benign prostatic hyperplasia (BPH).