Delusions are categorized into four different groups:

• Bizarre delusion: Delusions are deemed bizarre if they are clearly implausible and not understandable to same-culture peers and do not derive from ordinary life experiences.[2] An example named by the DSM-5 is a belief that someone replaced all of one's internal organs with someone else's without leaving a scar, depending on the organ in question.
• Non-bizarre delusion: A delusion that, though false, is at least technically possible, e.g., the affected person mistakenly believes that they are under constant police surveillance.
• Mood-congruent delusion: Any delusion with content consistent with either a depressive or manic state, e.g., a depressed person believes that news anchors on television highly disapprove of them, or a person in a manic state might believe they are a powerful deity.
• Mood-neutral delusion: A delusion that does not relate to the patient's emotional state; for example, a belief that an extra limb is growing out of the back of one's head is neutral to either depression or mania.

Themes In addition to these categories, delusions often manifest according to a consistent theme. Although delusions can have any theme, certain themes are more common. Some of the more common delusion themes are:

• Delusion of control: False belief that another person, group of people, or external force controls one's general thoughts, feelings, impulses, or behaviors.
• Cotard delusion: False belief that one does not exist or that one has died. Some cases also include the belief that one is immortal or that one has lost their internal organs, blood, or other body parts.
• Delusional jealousy: False belief that a spouse or lover is having an affair, with no proof to back up the claim.
• Delusion of guilt or sin (or delusion of self-accusation): Ungrounded feeling of remorse or guilt of delusional intensity.
• Thought broadcasting: False belief that other people can know one's thoughts.
• Delusion of thought insertion: Belief that another thinks through the mind of the person.
• Persecutory delusions: False belief that one is being persecuted.
• Delusion of reference: False belief that insignificant remarks, events, or objects in one's environment have personal meaning or significance. Usually the meaning assigned to these events is negative, but the 'messages' can also have a grandiose quality.
• Erotomania: False belief that another person is in love with them.
• Religious delusion: Belief that the affected person is a god or chosen to act as a god.
• Somatic delusion: Delusion whose content pertains to bodily functioning, bodily sensations or physical appearance. Usually the false belief is that the body is somehow diseased, abnormal or changed. A specific example of this delusion is delusional parasitosis: Delusion in which one feels infested with insects, bacteria, mites, spiders, lice, fleas, worms, or other organisms.
• Delusion of poverty: Person strongly believes they are financially incapacitated. Although this type of delusion is less common now, it was particularly widespread in the days preceding state support.