summary There are limits to what can be achieved with the instruments for measuring psychotic disorders. However, the diagnosis of psychotic disorders is supported by various semi-structured diagnostic interviews. The severity of the various symptom dimensions can be measured adequately according to several scales. Effective instruments are available for evaluating neurological and somatic side effects and a patient's subjective experience. It is advisable to make regular assessments of symptom severity, unwanted medications effects and the patient's needs.