Background: Children and adolescents are the potential capitals of communities. Therefore, their physical, mental, social, and spiritual health is of great importance. Objectives: This study aimed to evaluate the prevalence of psychiatric disorders among children and adolescents in Southern Khorasan province, Iran. Methods: This cross-sectional descriptive-correlational study was conducted in 2017. Study population consisted of children and adolescents aged 6-18 who lived in Southern Khorasan province, Iran. A sample of 1029 children and adolescents was selected through multistage cluster sampling. Data were collected using the Kiddie Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version (K-SADS-PL) and analyzed using the SPSS software (v. 19.0) and by conducting the Fisher's exact test. Results: The overall prevalence of psychiatric disorders among children and adolescents in Southern Khorasan province, Iran, was 15.2%. The prevalence of these disorders among male and female participants was 15.5% and 14.8%, respectively. Moreover, the prevalence was 13.1% in the 6-9 age group, 15.5% in the 10-14 age group, and 17% in the 15-18 age group. In addition, the prevalence of psychiatric disorders among participants who lived in urban and rural areas was 18.9% and 6.3%, respectively. The most prevalent psychiatric disorders were respectively separation anxiety (5.2%), obsessive-compulsive disorder (3.5%), generalized anxiety disorder (3%), enuresis (2.9%), oppositional defiant disorder (2.4%), depression, special phobias, attention deficit-hyperactivity disorder (1.6%), agoraphobia (1%), and social phobia (0.8%). Conclusions: Need-based age-appropriate mental health services are needed to promote mental health among children and adolescents.