Population studies on the prevalence of temporomandibular disorders (TMD) and their associations with quality of life (QoL), emotional states and sleep quality in South-East Asian youths are not available. This cross-sectional study assessed the presence of TMD and their relationships to QoL, depression, anxiety, stress and sleep quality in a cohort of South-East Asian adolescents/young adults. Three hundred and sixty-two students from a polytechnic were enrolled in the study and completed an online questionnaire consisting of the Fonesca's Anamnestic Index (FAI), Oral Health Impact Profile for TMD (OHIP-TMD), Depression, Anxiety and Stress Scales-21 (DASS-21) and Pittsburgh Sleep Quality Index. The FAI appraises TMD severity while OHIP-TMD determines the effect of TMD on oral health-related QoL. Statistical analysis was performed using chi-square test for categorical data whilst one-way ANOVA/post hoc Bonferroni's tests were employed for numerical scores (P < 0.05). Of the 244 participants who completed the questionnaires in their entirety (37 males; 207 females, mean age 20.1 ± 3.2 years), 32.4% had mild TMD, 9.4% had moderate TMD and 58.2% were TMD free. The total prevalence of TMD was 41.8% (n = 102) and most OHIP-TMD domains including functional limitation (P = 0.000), physical pain (P = 0.000), handicapped (P = 0.000) and psychological discomfort (P = 0.001) showed significant differences in mean scores depending on TMD severity. A similar trend was observed for DASS-21. The majority of participants with TMD (69.6%; n = 71) had poor sleep quality (P = 0.004). TMD appear to be prevalent in South-East Asian youths with varying severity. Severity of TMD had some bearing on QoL, emotional states as well as sleep quality.