Schizotypal personality disorder (StPD or SPD), also known as schizotypal disorder, is a mental disorder characterized by thought disorder, paranoia, a characteristic form of social anxiety, derealization, transient psychosis, and unconventional beliefs. People with this disorder often feel pronounced discomfort in forming and maintaining social connections with other people, primarily due to the belief that other people harbor negative thoughts and views about them. People with StPD may react oddly in conversations, such as not responding as expected, or talking to themselves. They frequently interpret situations as being strange or having unusual meanings for them; paranormal and superstitious beliefs are common.

The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) classifies StPD as a personality disorder belonging to cluster A, which is a grouping of personality disorders exhibiting traits such as odd and eccentric behavior. In the International Classification of Diseases, the latest edition of which is the ICD-11, schizotypal disorder is not classified as a personality disorder, but among psychotic disorders.

People with StPD usually disagree with the suggestion that their thoughts and behaviors are a 'disorder' and seek medical attention for depression or anxiety instead. Schizotypal personality disorder occurs in approximately 3% of the general population and is more commonly diagnosed in males.

Odd and magical thinking is common among people with StPD. They are more likely to believe in supernatural phenomena and entities. It is common for people with StPD to experience severe social anxiety and have paranoid ideation. Ideas of reference are common in people with StPD. They can feel as if expressing themselves is dangerous. They may also feel that others are more competent, and have deeply entrenched and pervasive insecurities. Strange thinking patterns may be a defense mechanism against these feelings. People with StPD usually have limited levels of self-awareness. They may believe others think of them more negatively than they actually do.

Patients with StPD can have difficulties in recognizing their or others' emotions, which can extend to difficulty expressing emotion. They may have limited responses to others' emotions and can be ambivalent. It is common for people with StPD to derive limited joy from activities. People with StPD are typically more socially isolated and uninterested in social situations than people without StPD, although they are still likely to be socially active on the Internet. Depersonalization, derealization, boredom, and internal fantasies are common in patients with StPD. Abnormal facial expressions are also common in people with StPD, and they can have aberrant eye movements and difficulty responding to stimuli. They are often more prone to substance abuse or suicidal ideation. In an epidemiological study on suicidal behavior in StPD, even when sociodemographic factors were accounted for, people with StPD were 1.51 times more likely to attempt suicide. StPD is also often characterized as having similar symptoms as schizophrenia, but with less severe cognitive deficits.

People with StPD tend to have cognitive impairments. They can have abnormal perceptional and sensory experiences such as illusions. For example, someone with StPD may perceive colors as lighter or darker than others perceive them. Facial perception may also be difficult for people with the disorder. They may see others as deformed, misrecognize them, or feel as if they are alien to them. People with StPD can have difficulty processing information such as speech or language. They are more likely to speak slowly, with less fluctuation in pitch, and long pauses between speech. Patients with StPD may have a lower odor detection threshold, and can have impaired auditory or olfactory processing. It is also common for people with StPD to struggle with context processing, which cause them to form loose connections between events. In addition, people with StPD can have decreased capacities for multisensory integration or contrast sensitivity, either hyperreactive or impaired reactions to sensory input, slower response times, impaired attention, poorer postural control, and difficulties with decision-making. They can have difficulties in memory, and may have frequent intrusive memories of events. It is common for people with StPD to feel déjà vu or as if they can accurately predict future events due to abnormalities in the brain's memory storage.

StPD was introduced in 1980 in the DSM-III. Its inclusion provided a new classification for schizophrenia-spectrum disorders and of personality disorders that were previously unspecified. Its diagnosis was developed through differentiating the classifications of borderline personality disorder, of which some of the diagnosed population demonstrated schizophrenia-spectrum traits. When the separation of borderline personality disorder and StPD was originally suggested by Spitzer and Endicott, Siever and Gunderson opposed the distinction. Siever and Gunderson's opposition to Spitzer and Endicott was that StPD was related to schizophrenia. Spitzer and Endicott stated "We believe, as do the authors, that the evidence for the genetic relationship between Schizotypal features and Chronic Schizophrenia is suggestive rather than proven". StPD was included in the DSM-IV and the DSM-5 and saw little change in its diagnosis.

The reported prevalence of StPD in community studies ranges from 1.37% in a Norwegian sample, to 4.6% in an American sample. A large American study found a lifetime prevalence of 3.9%, with somewhat higher rates among men (4.2%) than women (3.7%). It may be uncommon in clinical populations, with reported rates of up to 1.9%. It has been estimated to be prevalent among up to 5.2% of the general population. Together with other cluster A personality disorders, it is also very common among homeless people who show up at drop-in centers, according to a 2008 New York study. The study did not address homeless people who do not show up at drop-in centers. Schizotypal disorder may be overdiagnosed in Russia and other post-Soviet states.