What is delusional disorder?

Delusional disorder, previously called paranoid disorder, is a type of serious mental illness — called a “psychosis”— in which a person cannot tell what is real from what is imagined. The main feature of this disorder is the presence of delusions, which are unshakable beliefs in something untrue. People with delusional disorder experience non-bizarre delusions, which involve situations that could occur in real life, such as being followed, poisoned, deceived, conspired against, or loved from a distance. These delusions usually involve the misinterpretation of perceptions or experiences. In reality, however, the situations are either not true at all or highly exaggerated.

People with delusional disorder often can continue to socialize and function quite normally, apart from the subject of their delusion, and generally do not behave in an obviously odd or bizarre manner. This is unlike people with other psychotic disorders, who also might have delusions as a symptom of their disorder. In some cases, however, people with delusional disorder might become so preoccupied with their delusions that their lives are disrupted.

Although delusions might be a symptom of more common disorders, such as schizophrenia, delusional disorder itself is rather rare. Delusional disorder most often occurs in middle to late life.

What are the types of delusional disorder?

There are different types of delusional disorder based on the main theme of the delusions experienced. The types of delusional disorder include:

  • Erotomanic. Someone with this type of delusional disorder believes that another person, often someone important or famous, is in love with him or her. The person might attempt to contact the object of the delusion, and stalking behavior is not uncommon.
  • Grandiose. A person with this type of delusional disorder has an over-inflated sense of worth, power, knowledge, or identity. The person might believe he or she has a great talent or has made an important discovery.
  • Jealous. A person with this type of delusional disorder believes that his or her spouse or sexual partner is unfaithful.
  • Persecutory. People with this type of delusional disorder believe that they (or someone close to them) are being mistreated, or that someone is spying on them or planning to harm them. It is not uncommon for people with this type of delusional disorder to make repeated complaints to legal authorities.
  • Somatic. A person with this type of delusional disorder believes that he or she has a physical defect or medical problem.
  • Mixed. People with this type of delusional disorder have two or more of the types of delusions listed above.

What causes delusional disorder?

As with many other psychotic disorders, the exact cause of delusional disorder is not yet known. Researchers are, however, looking at the role of various genetic, biological, and environmental or psychological factors.

  • Genetic. The fact that delusional disorder is more common in people who have family members with delusional disorder or schizophrenia suggests there might be a genetic factor involved. It is believed that, as with other mental disorders, a tendency to develop delusional disorder might be passed on from parents to their children.
  • Biological. Researchers are studying how abnormalities of certain areas of the brain might be involved in the development of delusional disorders. An imbalance of certain chemicals in the brain, called neurotransmitters, also has been linked to the formation of delusional symptoms. Neurotransmitters are substances that help nerve cells in the brain send messages to each other. An imbalance in these chemicals can interfere with the transmission of messages, leading to symptoms.
  • Environmental/psychological. Evidence suggests that delusional disorder can be triggered by stress. Alcohol and drug abuse also might contribute to the condition. People who tend to be isolated, such as immigrants or those with poor sight and hearing, appear to be more vulnerable to developing delusional disorder.

What are the symptoms of delusional disorder?

The presence of non-bizarre delusions is the most obvious symptom of this disorder. Other symptoms that might appear include:

  • An irritable, angry, or low mood
  • Hallucinations (seeing, hearing, or feeling things that are not really there) that are related to the delusion (For example, a person who believes he or she has an odor problem may smell a bad odor.)

Last reviewed by a Cleveland Clinic medical professional on 01/22/2018.


  • American Psychiatric Association (Corporate Author). Diagnostic and Statistical Manual of Mental Disorders, DSM-5. American Psychiatric Publishing, Incorporated; 2013.
  • Blazer DG, Steffens DC. The American Psychiatric Publishing Textbook of Geriatric Psychiatry. American Psychiatric Pub; 2009.
  • Shelton RC. Chapter 17. Other Psychotic Disorders. In: Ebert MH, Loosen PT, Nurcombe B, Leckman JF. eds. CURRENT Diagnosis & Treatment: Psychiatry, 2e. New York: McGraw-Hill; 2008.
