Paranoia is a syndrome in which a person thinks or believes, without justification, that other people are plotting or conspiring against him, are harassing him, or are otherwise persecuting or trying to harm him in some way.

Paranoid thinking frequently causes a person to interpret or exaggerate innocuous or trivial incidents in a self-referent way; e.g., to see two people talking at a distance and to irrationally assume that they are plotting against or criticizing him.

Grandiosity or delusions of grandeur, which consist of exaggerated and unjustified ideas of a person's own importance, wealth, or power, frequently coexist with the classic persecutory orientation in paranoia.

Paranoia or paranoid thinking can be a prominent or primary feature in schizophrenia (paranoid schizophrenia), personality disorders, senile dementias, affective disorders, and manic-depressive psychoses, and indeed it is difficult to demarcate strictly what the DSM-III defines as paranoid disorders proper.

Persons with paranoid disorders may be otherwise normal people who are simply abnormally suspicious, or they may have an unshakable and highly elaborate delusional system involving worldwide conspiracies against them.

A special type of paranoia is delusional jealousy, in which a person delusionally believes or suspects that his spouse is having sexual relations with someone else.

A paranoid disorder can seriously impair an individual's social or marital functioning, but his thinking remains clear and orderly, his intellectual functioning is impaired only minimally or not at all, and the core of his personality remains intact.

Many people with paranoid disorders can have normal or near-normal careers.

The treatment of persons with paranoid disorders involves the use of antipsychotic drugs, frequently on a long-term maintenance basis.