A 61− year-old man in good health was found to have an elevated serum prostate-specific antigen level (8.9 mg/mL) on routine physical examination. Results of a digital rectal examination and transrectal ultrasound of the prostate were normal. Sextant needle biopsy specimens of the prostate were obtained, and the changes in one core from the right side were interpreted as moderately differentiated adenocarcinoma (Gleason grade 3 + 3 = 6). He underwent radical retropublic prostatectomy and bilateral pelvic lymphadenectomy; no cancer was indentified in the surgical specimen despite carful examination, Reevaluation of the diagnostic needle biopsy specimen revealed an irregular lobular cluster of small acini, which was reinterpreted as postatrophic hyperplasia (PAH), a histophathologic mimic of cancer. The small acini were lined by cuboidal coithelial cells with basophilic cytoplasm, slightly enlarged nuclei, and microunclcli, Basal cells were present but inconspicuous, Immunostaining with antibodies directed against high molecular weight cytokeratins demonstrated an intact but discontinuous basal cell layer. Postatrophic hyperplasia can be distinguished from adenocarcinoma by its charactenstic architecture, the presence of a basal cell layer, inconspicuous nucleoli, and the presence of adjacent acinar atrophy, Distinguishing PAH from carcinorna on needle biopsy speciment is especially difficult when only a portion of the lesion is sampled. Familiarily with this lesion should prevent misinterpretation as adenocarcinoma.