Objective: To investigate the prevalence and clinical characteristics of temporomandibular disorders (TMD) in a population prior to orthodontic treatment and to evaluate the possible risk factors for TMD. Methods: Clinical documentations and radiographs of 9,909 patients with malocclusions were retrospectively reviewed. All the patients were from the Orthodontic Department of Peking University School and Hospital of Stomatology during January 1998 to December 2003. The prevalence of TMD was calculated and the clinical characteristics were investigated. The association between the prevalence and the potential risk factors including aging, gender and malocclusion classifications was analysed using the method of chi-square and multivariate logistic regression analysis. Results: The prevalence of TMD was 8.6% in this population and statistically higher in females (9.5%) than in males (7.0%) (χ2 = 18.125, P 0.01). The prevalence had a positive association with age and increased in adolescence and young adulthood (χ2 = 157.503, P 0.01). Patients with Angle II malocclusion were more likely to suffer TMD than patients with Angle I malocclusion (odds ratio [OR] = 1.445, P 0.01). Conclusion: Aging, female gender and Angle II malocclusion were risk factors for the occurrence of TMD in the population. Keywords: temporomandibular disorders, orthodontics, risk factor