Abstract: Objective To determine the prevalence and distribution of malocclusion in primary and middle schoolchildren of Urumqi. Methods Using the stratified and cluster random sampling, 3 006 multinational primary and middle schoolchildren aged from 7-15 years in Urumqi were chosen. At the standard of Angle′s classification and individual normal occlusion, a full clinical examination was carried out. Results Of all the 3 006 subjects, there were 1 447 malocclusion cases according to the Angle′s classification, and the overall prevalence of malocclusion was 48.14%. Among them, 1 079 cases belonged to Angle′sⅠ（74.57%）, 175 cases belonged to Angle′s Ⅱ（12.09%）, and 193 cases belonged to Angle′s Ⅲ（13.34%）. There was statistically significant difference between males（54.63%） and females（42.19%） in their overall prevalence of malocclusion（P <0.05）. The prevalence of the Han, Uygur, Hazakh and Hui people were 43.28%, 51.37%, 40.38% and 52.81% respectively, and there were significant differences among the four main nationalities（P<0.05）. The prevalence distribution in three different
age spans（7-9, 10-12, and 13-15） was 41.64%, 47.81% and 50.62% respectively, and still had statistical significance（P<0.05）. From the malocclusion traits detected, the crowding of dentition was the main malocclusion, and others in turn were deep over bite, abnormal space of anterior, deep over jet, cross jet（including edge to edge bite）, etc. Conclusion The prevalence of malocclusion of primary and middle schoolchildren in Urumqi is higher, and it is different in the nationality, sex, and age. The research may help with the prevention and therapy about malocclusion.

Key words: malocclusion, prevalence, Angle′s classification, individual normal occlusion