Delusional jealousy, Morbid jealousy, or Othello syndrome is a psychiatric disorder in which a person holds a delusional belief that their spouse or sexual partner is being unfaithful.
The name Othello syndrome comes from the character in Shakespeare's play Othello, who murders his wife based on his false belief that she has been disloyal.
An affected person typically makes repeated accusations of infidelity based on insignificant or minimal evidence, often citing seemingly normal or everyday events or material to back up their claim. They may also take great pains to test their partner's fidelity and can go to considerable lengths to monitor their behavior and movements. This may be taken to extremes, such as "private-eye" type surveillance outside of the partner's residence or workplace, following them into the bathroom in case their partner has an illicit meeting or even hearing the voice of the perceived lover. Delusional jealousy is more often found in males than females, and it can occur regardless of an individual's sexual orientation.
Unlike other delusional disorders, delusional jealousy has a strong association with violence and in some cases stalking behavior. At the very least affected individuals tend to be irritable and confrontational.
It can be found in the context of schizophrenia and delusional disorder, such as bipolar disorder, but is also associated with alcoholism and sexual dysfunction and has been reported after neurological illness.