Orthodontic extrusion of teeth with advanced periodontal disease was evaluated in beagle dogs. Surgical destruction of one third to one half of the attachment apparatus and the inducement of chronic periodontal disease was accomplished on the hemisected mesial roots of the mandibular premolars. The roots on one side of the mandible were extruded toward a cemented stainless steel bridge by means of elastics providing 20 to 25 gm of force. The force was examined daily. When extruded teeth came into contact with the bridge, they were ligated in place for 21 days of stabilization. Clinical results showed that control teeth maintained their position and signs of advanced periodontitis. Extruded teeth had shallower pocket depths, less gingival inflammation, and no bleeding on probing. Radiographic evaluation showed no demonstrable changes in the control teeth. Early in the extrusion process, the teeth appeared to be avulsed, with more than three fourths of the root coronal to the alveolar crest. After stabilization, approximately 2 mm of new bone was seen coronal to the original alveolar crest, and the periapical areas had filled in as well. This bone formation was verified histologically. The extruded teeth had an intact attachment apparatus with all components in the same relative position on the teeth as in the controls. However, a shallower sulcus and less gingival inflammation were noted in the extruded teeth. There were statistically significant findings of a wider periodontal ligament space, greater cementum width, and increased bone height in the crestal areas of extruded teeth. Extruded teeth also had less cementum width and greater new bone formation at the apex. These findings demonstrate that orthodontic extrusion of teeth with advanced periodontal disease can have positive clinical and histologic results.