Child and adolescent psychiatry (or pediatric psychiatry) is a branch of psychiatry that focuses on the diagnosis, treatment, and prevention of mental disorders in children, adolescents, and their families. It investigates the biopsychosocial factors that influence the development and course of psychiatric disorders and treatment responses to various interventions. Child and adolescent psychiatrists primarily use psychotherapy and/or medication to treat mental disorders in the pediatric population.

There are many classifications of disorders. Developmental disorders include autism spectrum disorder and learning disorders, and some attention and behaviors disorders are attention deficit hyperactivity disorder, oppositional defiant disorder, and conduct disorder. Childhood schizophrenia is an example of a psychotic disorder. Major depressive disorder, bipolar disorder, persistent depressive disorder, and disruptive mood dysregulation disorder are under the classification of mood disorders.

A wide range of disorders that are classified as eating disorders include anorexia nervosa, bulimia nervosa, binge eating disorder, avoidant/restrictive food intake disorder (ARFID), and pica. Some anxiety disorders are panic disorder, phobias, and Generalized anxiety disorder. Lastly, substance use disorders can be specified to specific substances, such as alcohol use disorder or cannabis use disorder.

Disorders are often comorbid. For example, an adolescent can be diagnosed with both major depressive disorder and generalized anxiety disorder. The incidence of psychiatric comorbidities during adolescence may vary by race, ethnicity and socioeconomic status, among other variables.

The psychiatric assessment of a child or adolescent starts with obtaining a psychiatric history by interviewing the young person and his/her parents or caregivers. The assessment includes a detailed exploration of the current concerns about the child's emotional or behavioral problems, the child's physical health and development, history of parental care (including possible abuse and neglect), family relationships and history of parental mental illness. It is regarded as desirable to obtain information from multiple sources (for example both parents, or a parent and a grandparent) as informants may give widely differing accounts of the child's problems. Collateral information is usually obtained from the child's school with regards to academic performance, peer relationships, and behavior in the school environment.

Psychiatric assessment always includes a mental state examination of the child or adolescent which consists of a careful behavioral observation and a first-hand account of the young person's subjective experiences. This assessment also includes an observation of the interactions within the family, especially the interactions between the child and his/her parents.

The assessment may be supplemented by the use of behavior or symptom rating scales such as the Achenbach Child Behavior Checklist or CBCL, the Behavioral Assessment System for Children or BASC, Conners Comprehensive Behaviour Rating Scale (used for diagnosis of ADHD), Millon Adolescent Clinical Inventory or MACI, and the Strengths and Difficulties Questionnaire or SDQ. While these instruments bring a degree of objectivity and consistency to the clinical assessment, the diagnosis of ADHD requires confirmation by a clinician experienced in the evaluation of youth with and without ADHD who supplements the findings with input from parents, teachers, and the youth themselves.

More specialized psychometric testing may be carried out by a psychologist, for example using the Wechsler Intelligence Scale for Children, to detect intellectual impairment or other cognitive problems which may be contributing to the child's difficulties.