Pathological jealousy, also known as morbid jealousy, is a psychological disorder characterized by a pervasive preoccupation with the belief that one's spouse or romantic partner is being unfaithful, despite the absence of any real or substantiated evidence. The condition encompasses two primary clinical subtypes: obsessional jealousy and delusional jealousy, the latter also referred to as Othello syndrome.

Obsessive jealousy is generally classified as a subtype of obsessive-compulsive disorder, reflecting recurrent, intrusive thoughts and compulsive behaviors related to concerns about infidelity. In contrast, delusional jealousy is recognized as a subtype of delusional disorder, involving fixed, false beliefs concerning a partner’s infidelity that are resistant to reason or contrary evidence.

This disorder is characterised by persistent suspicions of a partner’s infidelity that are not supported by the evidence. Individuals affected by the condition may misinterpret neutral behaviour as indications of unfaithfulness, which further reinforces their perceptions.

Some studies have suggested that the disorder may co-occur with other conditions,including psychiatric disorders such as schizophrenia and delusional disorder, as well as mood disorders such as bipolar disorder. It has also been associated with certain behaviours, including stalking, cyberstalking, sabotage, alcoholism ,sexual dysfunction, and neurological disorders such as Parkinson's disease.

Pathological jealousy is generally identified through clinical assessment and is recognised as a possible feature of certain psychiatric conditions. According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), it may be observed in disorders such as obsessive-compulsive obsessive-compulsive disorder and delusional disorder. While it is not classified as a distinct diagnostic category, pathological jealousy is often viewed as a manifestation of underlying mental health issues.

The term "Othello Syndrome" is derived from the central character in Shakespeare’s tragedy Othello. In the play, Othello kills his wife Desdemona in the mistaken belief that she has been unfaithful to him. However, some scholars and experts have pointed out that Othello's actions resulted from manipulation and misinformation, which did not exhibit the clinical features of delusional disorder.

Clinical assessment of pathological jealousy requires a comprehensive assessment of the psychiatric history, encompassing the following areas:

Morbid jealousy has been associated with a range of psychological factors. In some cases, it is conceptualized as a delusional state. According to Kingham and Gordon, “Delusions of infidelity exist without any other psychopathology and may be considered to be morbid jealousy in its ‘purest’ form.” The condition is often characterized by distorted memory processing and misinterpretation of a partner’s behavior, leading to a fixed conviction of betrayal despite the absence of objective evidence.