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 lifestyle, 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 (such as schizotypal personality disorder) 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.
Others view them as indecisive in their actions, self-absorbed, absent-minded and detached from their surroundings. Excessive daydreaming is often present. In cases with severe defects in the capacity to form social relationships, dating and marriage may not be possible. ICD-10 criteria
The Classification of Mental and Behavioural Disorders of ICD-10 lists SzPD under (F60.1).The general criteria of personality disorder (F60) should be met first. In addition, at least four of the following criteria must be present:

Few, if any, activities provide pleasure. Displays emotional coldness, detachment, or flattened affectivity. Limited capacity to express warm, tender feelings for others as well as anger. Appears indifferent to either praise or criticism from others. Little interest in having sexual experiences with another person (taking into account age). Almost always chooses solitary activities. Excessive preoccupation with fantasy and introspection. Neither desires, nor has, any close friends or confiding relationships (or only one). Marked insensitivity to prevailing social norms and conventions; if these are not followed, this is unintentional. Guntrip criteria
Ralph Klein, Clinical Director of the Masterson Institute, delineates the following nine characteristics of the schizoid personality as described by Harry Guntrip:: 13–23 
Introversion
Withdrawnness
Narcissism
Self-sufficiency
A sense of superiority
Loss of affect
Loneliness
Depersonalization
RegressionThe description of Guntrips nine characteristics should clarify some differences between the traditional DSM portrait of SzPD and the traditional informed object relations view. All nine characteristics are consistent. Most, if not all, must be present to diagnose a schizoid disorder. Millons subtypes
Theodore Millon restricted the term "schizoid" to those personalities who lack the capacity to form social relationships.