Background:The prevalence of temporomandibular disorder (TMD) in children and adolescents is in the range of 6-68% and can be triggered or aggravated by emotional stress.Aim:The study was to investigate the prevalence of TMD in Portuguese children and adolescents and its association with emotional stress.Materials and Methods:The sample comprised 3,260 students aged 5-19 years. The questionnaire was used to assess the presence of TMD, and was applied in a single moment.Results:TMD was observed in 821 (25.2%) students. The most common symptoms of TMD were: if considered tense or nervous (52%), have headaches (36.8%), and habit of clenching or grinding teeth (27.3%). The girls had a 1.36 higher probability of developing TMD than boys (95% CI: 1.14-1.63; p < 0.001); moreover, students from the older age group had a 2.31 higher probability of developing the disorder (95% CI: 1.85-2.89; p < 0.001). Students who considered themselves tense or nervous presented 8.74 higher probability (95% CI: 7.03-10.86; p < 0.001) of developing TMD.Conclusion:This study showed a high prevalence of TMD in children and adolescents in southern Portugal, and revealed a significant association between this dysfunction and the levels of emotional stress. Female students, older students, and those considered tense or nervous have a higher probability of developing TMD.