There is no single type of delusional disorder, although they all share a common feature. This is that the delusions are considered "nonbizzare," in that the delusions could occur in real life. Most delusions fall into four main subtypes. These are persecutory type, grandiose type, jealous type, eroticmatic type, and somatic type. In persecutory type, the person believes that someone is planning to hurt him or her or that someone is mistreating him or her. In grandiose type, the person believes him or herself to be someone very important or with high levels of power, knowledge, or ability. In the jealous type, the person believes that a partner is being unfaithful. In Eroticmatic type, the person believes that someone, often famous or well known, is in love with him or her. In the somatic type, the person believes that he or she has a physical abnormality or disorder. Finally, a rare type of the disease is called a "folie à deux." In this instance, two people who are close to one another share a delusion.

People who suffer from delusional disorder tend to be in their forties. This disorder is difficult to treat because those suffering believe their delusions are real and do not believe they need treatment. They often to do not realize they have a delusion unless friends and family point it out. Even then, many people resist treatment. Researchers believe that the disorder stems from early life experiences and may not be genetic. However, there is a higher occurrence among first-degree relatives, which could suggest a biological component. Family relationships among those with the disorder tend to be stressful. When treatment does occur, antipsychotic medications and psychotherapy is used.