A psychotic disorder characterized by persisting non-bizarre delusions in the absence of other psychotic symptoms. The disorder cannot be caused by an identified medical condition or the effects of a substance, and cannot be diagnosed in an individual who has a previous history of schizophrenia or other psychotic disorder.

any mental disorder in which delusions play a significant role

a mental disorder characterized by a fixed false belief.

Delusional disorder is a psychiatric diagnosis denoting a psychotic mental illness that involves holding one or more non-bizarre delusions in the absence of any other significant psychopathology (signs or symptoms of mental illness). In particular a person with delusional disorder has never met any other criteria for schizophrenia and does not have any marked hallucinations, although tactile (touch) or olfactory (smell) hallucinations may be present if they are related to the theme of the delusion.