The Diagnostic and Statistical Manual of Mental Disorders (DSM) defines six subtypes of the disorder characterized as erotomanic (belief that someone is in love with one), grandiose (belief that one is the greatest, strongest, fastest, richest, or most intelligent person ever), jealous (belief that one is being cheated on), persecutory (delusions that the person or someone to whom the person is close is being malevolently treated in some way), somatic (belief that one has a disease or medical condition), and mixed, i.e., having features of more than one subtype.Delusions also occur as symptoms of many other mental disorders, especially the other psychotic disorders. The DSM-IV and psychologists agree that personal beliefs should be evaluated with great respect to cultural and religious differences, since some cultures have widely accepted beliefs that may be considered delusional in other cultures.An earlier, now obsolete, nosological name for delusional disorder was "paranoia". Classification
The International Classification of Diseases classifies delusional disorder as a mental and behavioural disorder. Diagnosis of a specific type of delusional disorder can sometimes be made based on the content of the delusions, to wit,  the Diagnostic and Statistical Manual of Mental Disorders (DSM) enumerates seven types:

Erotomanic type (erotomania): delusion that another person, often a prominent figure, is in love with the individual. The individual may breach the law as they try to obsessively make contact with the desired person. Grandiose type (megalomania): delusion of inflated worth, power, knowledge, identity or believing oneself to be a famous person, claiming the actual person is an impostor or an impersonator.
An attempt to contradict the belief is likely to arouse an inappropriately strong emotional reaction, often with irritability and hostility. They will not accept any other opinions. The belief is, at the least, unlikely, and out of keeping with the individuals social, cultural, and religious background. The person is emotionally over-invested in the idea and it overwhelms other elements of his or her psyche. The delusion, if acted out, often leads to behaviors which are abnormal, and out of character, although perhaps understandable in light of the delusional beliefs. Other people who know the individual observe that the belief and behavior are uncharacteristic and alien.Additional features of delusional disorder include the following:
It is a primary disorder. It is a stable disorder characterized by the presence of delusions to which the patient clings with extraordinary tenacity. The illness is chronic and frequently lifelong. The delusions are logically constructed and internally consistent. The delusions do not interfere with general logical reasoning (although within the delusional system the logic is perverted) and there is usually no general disturbance of behavior. If disturbed behavior does occur, it is directly related to the delusional beliefs. The individual experiences a heightened sense of self-reference. Events which, to others, are nonsignificant are of enormous significance to him or her, and the atmosphere surrounding the delusions is highly charged.However this should not be confused with gaslighting, where a person denies the truth, and causes the one being gaslit to think that they are being delusional.