Schizophrenia and delusional disorder can also be distinguished from schizoid personality disorder. The formers are characterized by a period of persistent psychotic symptoms, such as delusions and hallucinations. Schizoid personality disorder must have been present before the onset of psychotic symptoms and must persist when the psychotic symptoms are in remission for it to actually be schizoid personality disorder. .
The diagnostic criteria for schizoid personality disorder offers a list of symptoms which the individual must have four or more of to be diagnosed with schizoid personality disorder. The list comprises of (1) a lack of desire and enjoyment of close relationships, including being part of a family, (2) an inclination for solitary activities, (3) little if any interest in sexual experiences with another person, (4) experiences pleasure in few, if any, activities, (5) lacks close friends or confidants other than first degree relatives, (6) appears indifferent to the praise or criticism of others, and (7) shows emotional coldness, detachment, or flattened affectivity.
The definition of schizoid personality disorder has varied greatly in the different editions of the Diagnostic and Statistical Manual of Mental Disorders. It was previously broadly defined, but now it is divided into three different categories: schizoid, avoidant and schizotypal personality disorders. Now the Manual defines schizoid personality disorder as a pervasive pattern of detachment from social relationships and a restricted range of expression of emotions in interpersonal settings, which begins by early adulthood. This definition describes an important and essential feature of schizoid personality disorder. This is because the pattern of detachment from social settings and restricted range of expression of emotions lead to a lack of desire for intimacy and close relationships. This means that schizoid personalities do usually do not have any close friends or confidants.