OBJECTIVE We investigated whether a relationship exists between the flow to maintain an erection obtained at cavernosometry and the alteration of intracavernous structures in impotent patients with corporeal veno-occlusive dysfunction and normal arterial inflow. METHODS Computerized histomorphometric analysis of smooth muscle and elastic fibers, and endothelial cells was compared to the flow necessary to maintain erection after intracavernous vasoactive drug injection in 18 patients with corporeal veno-occlusive dysfunction. RESULTS A significant correlation between percentage of smooth muscle fibers and flow to maintain erection was observed, while no correlation was noted with elastic fibers and endothelial cells. CONCLUSIONS Corporeal veno-occlusive dysfunction seems to be due mainly to smooth muscular alterations. According to this observation treatment of impotent patients with this abnormality should not be restricted to the penile veins but should also include the intracavernous structures, predominantly the muscular component.