Schizoid personality disorder (, often abbreviated as SzPD or ScPD) is a personality disorder characterized by a lack of interest in social relationships, a tendency toward a solitary or sheltered life style, secretiveness, emotional coldness, detachment, and apathy. Affected individuals may be unable to form intimate attachments to others and simultaneously possess a rich and elaborate but exclusively internal fantasy world. Other associated features include stilted speech, a lack of deriving enjoyment from most activities, feeling as though one is an "observer" rather than a participant in life, an inability to tolerate emotional expectations of others, apparent indifference when praised or criticized, a degree of asexuality, and idiosyncratic moral or political beliefs.

Symptoms typically start in late childhood or adolescence. The cause of SzPD is uncertain, but there is some evidence of links and shared genetic risk between SzPD, other cluster A personality disorders, and schizophrenia. Thus, SzPD is considered to be a "schizophrenia-like personality disorder". It is diagnosed by clinical observation, and it can be very difficult to distinguish SzPD from other mental disorders or conditions (such as autism spectrum disorder, with which it may sometimes overlap).

The effectiveness of psychotherapeutic and pharmacological treatments for the disorder has yet to be empirically and systematically investigated. This is largely because people with SzPD rarely seek treatment for their condition. Originally, low doses of atypical antipsychotics were also used to treat some symptoms of SzPD, but their use is no longer recommended. The substituted amphetamine bupropion may be used to treat associated anhedonia. However, it is not general practice to treat SzPD with medications, other than for the short-term treatment of acute co-occurring disorders (e.g. depression). Talk therapies such as cognitive behavioral therapy (CBT) may not be effective, because people with SzPD may have a hard time forming a good working relationship with a therapist.

SzPD is a poorly studied disorder, and there is little clinical data on SzPD because it is rarely encountered in clinical settings. Studies have generally reported a prevalence of less than 1%. It is more commonly diagnosed in males than in females. SzPD is linked to negative outcomes, including a significantly compromised quality of life, reduced overall functioning even after 15 years, and one of the lowest levels of "life success" of all personality disorders (measured as "status, wealth and successful relationships"). Bullying is particularly common towards schizoid individuals. Suicide may be a running mental theme for schizoid individuals, though they are not likely to attempt it. Some symptoms of SzPD (e.g. solitary lifestyle, emotional detachment, loneliness, and impaired communication), however, have been stated as general risk factors for serious suicidal behavior.