What Is a Psychological Disorder?

Definition, Diagnosis and Prevalence

What exactly is a psychological disorder? How is a psychological disorder diagnosed? Learn more about how clinicians define and classify mental disorders and discover how many people are impacted by such disorders every year.

What Is a Psychological Disorder?

A psychological disorder, also known as a mental disorder, is a pattern of behavioral or psychological symptoms that impact multiple life areas and/or create distress for the person experiencing these symptoms.

How are Psychological Disorders Diagnosed?

The classification and diagnosis is an important concern for both mental health providers and mental health clients. While there is no single, definitive definition of mental disorders, a number of different classification and diagnostic criteria have emerged. Clinicians utilize the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV TR), published by the American Psychiatric Association, to determine whether a set of symptoms or behaviors meets the criteria for diagnosis as a psychological disorder. The International Classification of Diseases (ICD-16), published by the World Health Organization, is also frequently used.

What Is the Purpose of Getting a Diagnosis?

While some people may avoid seeking a diagnosis out of fear of social stigma, getting a diagnosis is an essential part of finding an effective treatment plan. A diagnosis is not about applying a label to a problem, it is about discovering solutions, treatments and information related to the problem.

How Prevalent Are Psychological Disorders?

Relatively recent research has revealed that psychological disorders are far more prevalent that previously believed. According to the National Institute of Mental Health (NIMH), approximately 26 percent of American adults over the age of 18 suffer from some type of diagnosable mental disorder in a given year.

The 1994 National Comorbidity Survey (NCS) indicated that 30 percent of respondents had experienced symptoms of at least one psychological disorder in the previous year. The survey also indicated that nearly half of all adults experience some form of mental disorder at some point in their life.

What Are the Different Types of Mental Disorders?

The DSM-IV TR describes approximately 250 different psychological disorders, most of which fall under a category of similar or related disorders. Some of the prominent diagnostic categories include eating disorders, mood disorders, somatoform disorders, sleep disorders, anxiety disorders and personality disorders.


Kessler, R.C., McGonagle, K.A., Zhoa, S., Nelson, C.B., Hughes, M., Eshleman, S., & others. (1994). Lifetime and 12-month prevalence of DSM-III-R psychiatric disorders in the United States: Results from the National Comorbidity Survey (NCS). Archives of General Psychiatry, 51, 8-19.

National Institute of Mental Health. (2008). The numbers count: Mental disorders in America. Found online at http://www.nimh.nih.gov/health/publications/the-numbers-count-mental-disorders-in-america/index.shtml#Intro