The clinical features, microbiologic investigation, and response to therapy of three patients with Gardnerella vaginalis-associated balanoposthitis were studied. Each man presented with a similar syndrome of diffuse erythema and pruritus of the glans meatus and coronal sulcus, irritation of the prepuce, and minimal urethral discharge. A characteristic fishy odor was present in the urethral discharge of all three patients. G. vaginalis was isolated from the glans of all three, and clue cells were present in two. In all cases, cultures for Candida albicans, herpes simplex virus, Neisseria gonorrhoeae, Chlamydia trachomatis, and Ureaplasma urealyticum were negative. All three patients responded to oral therapy with metronidazole and concurrent treatment of the partner. Two patients subsequently relapsed but ultimately responded to clindamycin therapy. These men presented with a distinctive clinical syndrome of balanoposthitis associated with G. vaginalis, which is in many respects similar to the syndrome of bacterial vaginosis in women. Our data indicate that balanoposthitis may have a polymicrobial and synergistic etiology involving G. vaginalis and anaerobic bacteria in the male lower genital tract; such an etiology is analogous to that of bacterial vaginosis.