Mesonephric remnant (MR) hyperplasia in the prostate is a rarely reported condition that is usually distinguished from prostatic adenocarcinoma by the absence of cytologic atypia as well as the absence of prostatic markers (prostate-specific antigen and prostatic acid phosphatase) expression. We report a case of prostatic MR hyperplasia with architectural and cytologic atypia in a 56-year-old man. The microscopic appearance strongly suggested malignancy, but immunohistochemistry allowed the diagnosis to be corrected. The presence of MRs in prostate tissues may be more common than appreciated or reported. Once the possibility is considered, the diagnosis is easily confirmed using immunochemistry.