Background:There has been a lack of prevalence estimates of DSM-5 mental disorders in child populations at the national level worldwide. Little is known about the disease burden of child mental disorders. Taiwan’s National Epidemiological Study of Child Mental Disorders (TNESCMD) was designed to address these research gap. This study reported the methodology of the TNESCMD and the lifetime and six-month prevalence of mental disorders according to the DSM-5 diagnostic criteria in Taiwanese children. I further compared the prevalence and estimated disease burden from the TNESCMD with Taiwan National Health Insurance Research Database (TNHIRD). Methods: The TNESCMD used stratified cluster sampling to select 69 schools in Taiwan resulting in a nationally representative sample. Among all 10118 eligible children selected via our sampling method, 9560 (94.4%) children, 6846 (67.6%) parents, and 9759 (96.3%) teachers participated in this study and completed the questionnaires. Among them, 4816 children in grades 3 (n=1352), 5 (n=1297), and 7 (n=2167) further underwent face-to-face psychiatric interviews using the Kiddie-Schedule for Affective Disorders and Schizophrenia-Epidemiological (K-SADS-E) version, modified for the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Clinical questionnaires for attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), emotional and behavioral problems included the Chinese version of the Swanson, Nolan, and Pelham IV scale, Social Responsiveness Scale, and Child Behavior Checklist were used to examine the convergent and divergent validity with K-SADS-E. Risk factor analysis for mental disorders included sex, age, urban/rural and community income. 1,389,372 participants aged 8 to 14 were randomly selected from the 2016 TNHIRD claims dataset. The disease burden was calculated regarding years lived with disability (YLDs) with adjustment for comorbidity. YLDs and their 95% uncertainty intervals (UI) were reported. A rates ratio (RR) was reported to depict the strength of YLDs difference between TNESCMD and TNHIRD. Results: The K-SADS-E showed satisfactory inter-rater reliability (prevalence adjusted bias adjusted kappa = .80-1.00) among eight interviewers. The diagnoses of K-SADS-E demonstrated good convergent and divergent validity with most corresponding clinical questionnaires. The weighted lifetime and 6-month prevalence rates for overall mental disorders were 32.3% and 25.8%, respectively. The most prevalent mental disorders (lifetime, 6-month) were anxiety disorders (15.1%, 13.5%) and ADHD (10.5%, 9.0%), followed by sleep disorders, tic disorder, oppositional defiant disorder, and ASD. New DSM-5 mental disorders, avoidant/restrictive food intake disorder and disruptive mood dysregulation disorder, were also found with current low prevalence (<1%). Boys were more likely to have neurodevelopmental disorders and disruptive and impulse-control, and conduct disorders, whereas girls were more likely to develop anxiety disorders, depressive disorder and anorexia nervosa. Depressive disorder and suicide-related problems were more prevalent in Grade 7 children. The participants living in urban areas and low socioeconomic communities had increased risks for mental disorders. The overall YLD from all mental disorders in the TNESCMD was 5.24 times (95% UI: 4.15-6.70) more than that in TNHIRD, with the lowest and highest YLDs RR for autism spectrum disorder (ASD; RR: 2.24 and 95% UI: 1.28-3.93) and anxiety disorders (RR: 351.00 and 95% UI: 175.05-703.80), respectively. Unlike ADHD and ASD, the total proportions explained by anxiety disorders and conduct disorder/oppositional defiant disorder were significantly lower in TNHIRD than those in the TNESCMD and Global Burden of Disease 2016. Conclusions: Our findings suggest that the Mandarin version of the K-SADS-E for DSM-5 is a reliable and valid instrument for diagnosing child and adolescent mental disorders based on DSM-5. Similar to the DSM-IV prevalence rates reported in Western countries, indicate that DSM-5 mental disorders are common in the Taiwanese child population. The comparatively higher estimate of the disease burden of mental disorders in children from community-based setting might provide the preparation of future financial resource allocation, development and management of medical service, and human resource for mental health care in the clinic-based settings. For disorders with a significant difference in disease burden between the community-based and clinic-based settings, they may need more mental health promotion and prevention.