A persecutory delusion is a type of delusional condition in which the affected person believes that harm is going to occur to oneself by a persecutor, despite a clear lack of evidence. The person may believe that they are being targeted by an individual or a group of people. Persecution delusions are very diverse in terms of content and vary from the possible, although improbable, to the completely bizarre. The delusion can be found in various disorders, being more usual in psychotic disorders.

Persecutory delusion is at the more severe end of the paranoia spectrum and can lead to multiple complications, from anxiety to suicidal ideation. Persecutory delusions have a high probability of being acted upon, for example not leaving the house due to fear, or acting violently. The persecutory delusion is a common type and is more prevalent in males.

Persecutory delusions can be caused by a combination of genetic (family history) and environmental (drug and alcohol use, emotional abuse) factors. This type of delusion is treatment-resistant. The most common methods of treatment are cognitive behavioral therapy, medications, namely first and second generation antipsychotics, and in severe cases, hospitalization. The diagnosis of the condition can be made using the DSM-5 or the ICD-11.

Persecutory delusions are persistent, distressing beliefs that one is being or will be harmed, that continue even when evidence of the contrary is presented. This condition is often seen in disorders like schizophrenia, schizoaffective disorder, delusional disorder, manic episodes of bipolar disorder, psychotic depression, and some personality disorders. Alongside delusional jealousy, persecutory delusion is the most common type of delusion in males and is a frequent symptom of psychosis. More than 70% of individuals with a first episode of psychosis reported persecutory delusions. Persecutory delusion is often paired with anxiety, depression, disturbed sleep, low self-esteem, rumination and suicidal ideation. High rates of worry, similar to those in generalized anxiety disorder, are present in individuals with the delusion, moreover the level of worry has been linked to the persistence of the delusion. People with persecutory delusion have an increased difficulty in attributing mental states to others and oftentimes misread others' intentions as a result.

People who present with this form of delusion are often in the bottom 2% in terms of psychological well-being. A correlation has been found between the imagined power the persecutor has and the control the sufferer has over the delusion. Those with a stronger correlation between the two factors have a higher rate of depression and anxiety. In urban environments, going outside leads people with this delusion to have a major increases in levels of paranoia, anxiety, depression and lower self-esteem. People with this delusion often live a more inactive life and are at a higher risk of developing high blood pressure, diabetes and heart disease, having a lifespan 14.5 years less than the average as a result.

Those with persecutory delusion have the highest risk of acting upon those thoughts compared to other type of delusions, such acts include refusing to leave their house out of the fear of being harmed, or acting violently due to a perceived threat. Safety behaviors are also frequently found — individuals who feel threatened perform actions in order to avert their feared delusion from occurring. Avoidance is commonly observed: individuals may avoid entering areas where they believe they might be harmed. Some may also try to lessen the threat, such as only leaving the house with a trusted person, reducing their visibility by taking alternative routes, increasing their vigilance by looking up and down the street, or acting as if they would resist attack by being prepared to strike out.

A study assessing schizophrenia patients with persecutory delusion found significantly higher levels of childhood emotional abuse within those people but found no differences of trauma, physical abuse, physical neglect and sexual abuse. Because individuals with the disorder tend to respond to the delusion with worry instead of challenging the content of the delusion, worry is responsible in developing and maintaining the persecutory thoughts on the individuals' minds. Biological elements, such as chemical imbalances in the brain and alcohol and drug use are a contributing factor to persecutory delusion. Genetic elements are also thought to influence, family members with schizophrenia and delusional disorder are at a higher risk of developing persecutory delusion.

Persecutory delusions are thought to be linked with problems in self-other control, that is, when an individual adjusts the representation of oneself and others in social interactions. Because of this shortcoming, the person might misattribute their own negative thoughts and emotions onto others. Another theory is that the delusional belief arises due to low self-esteem. When a threat appears, the person protects themselves from negative feelings by blaming others.