Objectives: To determine whether there was a prevalent tendency for intermaxillary tooth size discrepancies among different malocclusion groups and genders in a group of Thai people. Methods: Samples consisted of 360 pretreatment orthodontic models with Class I, II and III malocclusions. Tooth size measurements were performed on these models by electronic digital calipers to an accuracy of 0.01 mm.Tooth size ratios were analyzed as described by Bolton. The incidence of mesio-distal tooth size discrepancies in the malocclusion groups was analyzed and compared between males and females. The ratios from this study were compared with the ratios form various studies, principally, Bolton's study. Results: The study showed no significant sexual dimorphism for the tooth size discrepancies in each of three malocclusion groups. Further, ANOVA indicated that no significant difference was determined in the anterior ratio but there were significant differences between Class II and both Class I , III malocclusion groups for posterior and overall ratios. When the anterior and overall ratios of the present study were compared to that of Bolton's, no significant difference was found in all malocclusion classes, except for the anterior ratio in Class III malocclusion. Conclusions: Intermaxilly tooth size discrepancies may affect to the finishing step of orthodontic treatment. The differences in intermaxillary tooth size discrepancy among the three malocclusion groups should be considered during orthodontic diagnosis and therapy.