Twenty-one patients who had undergone orthodontic treatment in combination with mandibular advancement surgery to treat Class II malocclusion and deep overbite were followed up. Median vertical relapse at the bony chin (after a mean followup of 16 months) was found to be 2.9 mm (4 4%). Sagittal advancement was found to have good stability; most of the patients exhibited some additional anterior movement of the chin during the follow-up period. At the same time, the entire mandible rotated counterclockwise and the gonial angle increased. Individual response to treatment varied greatly; two patients exhibited major horizontal relapse. Controlling the position of the mandibular proximal segment seemd to be th e most important factor in posttreatment stability of this sample.