Nephrogenic adenoma (NA) is a benign lesion of the urinary tract associated with injury to the urothelium. The varied morphologic patterns of NA make it a potential diagnostic pitfall, because it can mimic closely prostatic adenocarcinoma and urothelial carcinoma. In current practice, an antibody cocktail comprising p63, CK903, and AMACR (PIN-4 cocktail) is frequently utilized to evaluate foci suspicious for prostatic adenocarcinoma. Although the staining characteristics of the individual components of the PIN-4 cocktail have been reported for NA, no study has described the expression patterns for NA when the stains are applied as a cocktail. GATA-3 is an emerging marker of urothelial carcinoma; however, the GATA-3 staining characteristics of NA have yet to be described. Sixty-three NA specimens (M:F=36:27, average age=51.4 y) from various locations in the urinary tract including urinary bladder (n=40), ureter (n=3), and urethra (n=20) were collected from the archives of 2 institutions. Immunohistochemical analysis with the PIN-4 cocktail and GATA-3 antibodies was performed, and the distribution and intensity of staining was recorded for each antibody in each case. PIN-4 cocktail staining revealed AMACR expression in 56% of cases, CK903 expression in 97%, and rare p63 positivity (in only 2 cases). Only 2 NA cases displayed an overall PIN-4 staining pattern compatible with prostate cancer. GATA-3 expression was noted in 40% of NAs. No correlation between AMACR, CK903, or GATA-3 positivity and histologic pattern or anatomic location was identified. Although heterogenous staining patterns were seen within individual cases, use of the PIN-4 cocktail effectively discriminates NA from prostate cancer because of the high frequency of coexpression of AMACR and CK903 within NA. In addition, GATA-3 is not a useful marker in differentiating between NA and urothelial carcinoma.