Lateral and anterior displacements of mandible may cause malocclusion. The aim of this study was to determine the prevalence of these displacements in a population of 597 childrens age 12 in Mashhad secondary schools. Displacment of mandible was shown to be in 11.8 percent of the population (6.2 percent anterior and 5.6 percent lateral displacement).Anterior displacement of mandible was diagnosed in all mandibie lateral displacements. Premature contacts were observed in upper lateral incisors, second premolars and first molar in anterior and lateral displacements, respectively.