The occurrence of diverticula in human seminiferous tubules was investigated in the adult human testis in normal as well as physiologic (aging) and pathologic (germ cell depletion, obstruction of male excretory ducts, varicocele and systemic arteriosclerosis) conditions. Diverticula, which are evaginations of the seminiferous epithelium surrounded by a thin tunica propria, were present in all groups studied. The number of diverticula per mm2 testis was higher in the testis with obstruction than in those without obstruction at each age considered. The number of diverticula increased with age in both the obstructed and nonobstructed testis. No changes in the number of diverticula per mm2 testis were found in relation to systemic arteriosclerosis or different degrees of germ cell depletion. Varicocele was only associated with increased numbers of diverticula when it was also associated with obstruction. The formation of diverticula in human seminiferous tubules seems to be an obstructive process related to increasing age.