The aim of this study was to determine the changes in head posture and hyoid bone position after mandibular setback osteotomy in Turkish adult Class III patients. Serial lateral cephalograms of 42 Turkish Class III patients (24 female, 18 male patients, mean age: 25.4+/-1.2 years) who underwent mandibular setback surgery were evaluated preoperatively, 1.2+/-0.6 years, 2.3+/-0.8 and 4.2+/-0.9 years postoperatively. A mean mandibular setback of 5.6+/-0.8mm was associated with a posterior and inferior movement of the hyoid bone and a significant flexion in the neck posture. Surgical correction of mandibular prognathism altered the position of the hyoid bone by downward repositioning carrying the root of the tongue downwards immediately postoperatively, but followed with a tendency to return to its original position.