Periodontal examinations were carried out preorthodontically and again 2 to 28 months after orthodontic uprighting of 20 molars (40 furcation areas) in 16 patients. Preorthodontically, patients presented with generalized periodontitis. Postorthodontically, nine of 20 buccal furcations had become more severe, one had improved, and ten remained unchanged. Lingually, nine worsened, and 11 had no change. Furcation area pocket depths increased in 35.0% of furcations, but did not change in 57.5%. Furcation root form was not associated with the degree of change. Possible mesial root extrusion was found in 60.0% of the uprighted molars. The molars showing root extrusion had furcations that increased in severity. Heavy uprighting forces contributed to extrusion, and some effect ma y have been due to periodontal inflammation and bone loss. Mandibular molars can be uprighted in patients with moderate periodontitis, but light intrusive forces in an inflammation-free environment are recommended.