Schizoid personality disorder (, often abbreviated as SPD) is a personality disorder characterized by a lack of interest in social relationships, a tendency towards a solitary or sheltered lifestyle, secretiveness, emotional coldness, detachment, and apathy. Affected individuals may be unable to form intimate attachments to others and simultaneously demonstrate a rich, elaborate, and exclusively internal fantasy world.
SPD is not the same as schizophrenia or schizotypal personality disorder, but there is some evidence of links and shared genetic risk between SPD, other cluster A personality disorders, and schizophrenia. Thus, SPD is considered to be a "schizophrenia-like personality disorder".
Critics argue that the definition of SPD is flawed due to cultural bias and that it does not constitute a mental disorder but simply an avoidant attachment style requiring more distant emotional proximity. If that is true, then many of the more problematic reactions these individuals show in social situations may be partly accounted for by the judgments commonly imposed on people with this style. However, it is important to note that impairment is mandatory for any behaviour to be diagnosed as a personality disorder. SPD seems to satisfy this criterion because it is linked to negative outcomes. These include a significantly compromised quality of life, smaller GAF scores even after 15 years, and one of the lowest levels of "life success" of all personality disorders (measured as "status, wealth, and successful relationships").
Schizoid personality disorder is a poorly studied disorder, and there is little clinical data on SPD because it is rarely encountered in clinical settings. The effectiveness of psychotherapeutic and pharmacological treatments for the disorder have yet to be empirically and systematically investigated.