The goal of the present study was to determine whether the clinical treatment results in terms of pocket probing depth reduction and attachment gain would be different following conventional periodontal flap surgery if, on the one hand, root surfaces were smoothed after plaque and calculus removal or, on the other hand, root surfaces were first thoroughly cleaned but then intentionally roughened. 13 adult patients with moderate periodontitis participated; the same patients acted as a unit of control. Evaluations were performed on a total of 224 sites on 81 anterior and premolar teeth. On the 41 test teeth (111 sites), a coarse diamond stone was used following traditional root planing to roughen the root surfaces. The 40 control teeth (113 sites) were cleaned and planed using Gracey curettes. Measurements performed 3 and 6 months post-surgery revealed significant reductions in probing depths at both "rough" and "smooth" sites. However, no differences between the 2 methods were detected. This was true also with regard to attachment gain. We conclude that striving for root surface smoothness during periodontal surgery appears unnecessary.