Our aim was to evaluate the efficacy of simultaneous gap arthroplasty and distraction osteogenesis (DO) in the treatment of unilateral ankylosis of the temporomandibular joint (TMJ) in patients with micrognathia. During the period January 2000-December 2006, 11 patients with unilateral ankylosis of the TMJ and micrognathia were treated with simultaneous gap arthroplasty, mandibular osteotomy, and implantation of a distractor. Mouth opening exercises were started on the first postoperative day and distraction on the fifth postoperative day. All patients had satisfactory mouth opening at follow-up, the mean (range) being 32.4 (28-37) mm in 13 to 58 months' follow-up. Mean length (range) of the mandibular body increased by DO was 12.4 (7-15) mm. Facial asymmetry was corrected and satisfactory occlusions achieved with the help of postoperative orthodontic treatment. We conclude that DO and gap arthroplasty can be used simultaneously in the treatment of patients with ankylosis of the TMJ and micrognathia.