Sample and methodology: sample of study comprises 300 pupils aged 12-15 years old, studying in Non At Sat secondary school in Vientiane, Laos. Method of study is cross sectioned description. All pupils were examined and taken impressed to make study cast for occlusion analysis. Goal of study is to describe reality of malocclusion in children aged 12-15 years old to make the plan for prevention and treatment. Result: Ratios of class I, class II and class III occlusion are 63 percent, 14 percent and 23 percent respectively. In group of class I occlusion: percentages of female is 54,0 percent and that of male is 46,0 percent. In group of class II occlusion: ratio of female is 55.8 percent, that of male is 44,2 percent. In group of class III occlusion: ratio of female is 65,7 percent, that of male is 34,3 percent. Conclusion: Percentage of malocclusion of sample is high. It means that orthodontic treatment need is so high and it is necessary to make a preventive program for children.