Prostatic adenocarcinoma of the small acinar type can be mimicked by benign proliferative lesions, such as atypical adenomatous hyperplasia (adenosis), sclerosing adenosis, nodular hyperplasia (cellular areas), lobular hyperplasia, basal cell hyperplasia, mesonephric hyperplasia, and nephrogenic adenoma. In our study, we describe another microacinar proliferation, which we have termed verumontanum mucosal gland hyperplasia (VMGH) because it occurs exclusively in the verumontanum and adjacent posterior urethra where the ejaculatory ducts and utricle empty into the urethra. We reviewed 341 radical prostatectomies and cystoprostatectomies done from 1988 through 1993 for prostate and bladder carcinoma, respectively. Forty-nine prostates (14%) from patients aged 47 to 87 contained foci of VMGH. Of a total of 88 foci, a single lesion was present in 19 cases and multiple lesion in 30 cases. Fifty-nine of the foci arose around the ejaculatory or prostatic ducts, 17 from around the utricle, and 13 from adjacent posterior urethral mucosa. Individual lesions were quantified as to the number of acini per focus as follows: 6 to 10 in 28 (1+), 11 to 25 in 29 (2+), 25 to 50 in 16 (3+), and more than 50 in 15 (4+). No crystalloids or intraluminal mucin were seen, but; intraluminal corpora amylacea, usually numerous, were present in 57 of the 88 voci. The microacini were frequently "back to back" architecturally. The lining epithelium consisted of bland cuboidal to columnar luminal cells with underlying basal cells. VMGH, a previously undescribed benign microacinar proliferation, occurs in a very restricted and specific location and appears to be unrelated to other lesions with which it may be confused.