Diagnosis
Screening
There are various methods of screening for schizotypal personality. The Schizotypal Personality Questionnaire (SPQ) measures nine traits of STPD using a  self-report assessment. The nine traits referenced are Ideas of Reference, Excessive Social Anxiety, Odd Beliefs or Magical Thinking, Unusual Perceptual Experiences, Odd or Eccentric Behavior, No Close Friends, Odd Speech, Constricted Affect, and Suspiciousness. A study found that of the participants who scored in the top 10th percentile of all the SPQ scores, 55% were clinically diagnosed with STPD. A method that measures the risk for developing psychosis through self-reports is the Wisconsin Schizotypy Scale (WSS). The WSS divides schizotypal personality traits into 4 scales for Perceptual Aberration, Magical Ideation, Revised Social Anhedonia, and Physical Anhedonia. A comparison of the SPQ and the WSS suggests that these measures should be cautiously used for screening purposes of STPD. STPD as a Personality Disorder
DSM-5
In the American Psychiatric Associations DSM-5, schizotypal personality disorder is defined as a "pervasive pattern of social and interpersonal deficits marked by acute discomfort with, and reduced capacity for, close relationships as well as by cognitive or perceptual distortions and eccentricities of behavior, beginning by early adulthood and present in a variety of contexts.
It is difficult to gain rapport with people with STPD due to the fact that increasing familiarity and intimacy usually increase their level of anxiety and discomfort.Group therapy is recommended for persons with STPD only if the group is well structured and supportive. Otherwise, it could lead to loose and tangential ideation. Support is especially important for schizotypal patients with predominant paranoid symptoms, because they will have a lot of difficulties even in highly structured groups. Comorbidity
Schizotypal personality disorder frequently co-occurs with major depressive disorder, dysthymia and social phobia. Furthermore, sometimes schizotypal personality disorder can co-occur with obsessive–compulsive disorder, and its presence appears to affect treatment outcome adversely. Some people with a clinical diagnosis of OCD have been found to also possess many schizotypal personality traits resulting in what can be called ‘schizotypal OCD’. Without proper treatment, STPD tendencies, such as magical thinking and paranoid ideation, could worsen the symptoms of OCD in an individual. There may also be an association with bipolar disorder. People with Gilles de la Tourette syndrome (GTS) can commonly possess some schizotypal traits.In terms of comorbidity with other personality disorders, schizotypal personality disorder has high comorbidity with schizoid and paranoid personality disorder, the other two Cluster A conditions. It also has significant comorbidity with borderline personality disorder and narcissistic personality disorder.Some schizotypal people go on to develop schizophrenia, but most of them do not. There are dozens of studies showing that individuals with schizotypal personality disorder score similar to individuals with schizophrenia on a very wide range of neuropsychological tests.