The assessment of psychopathy in (forensic) schizophrenia spectrum disorders is long-standing debate. In the present study, we investigated the psychometric properties of the Comprehensive Assessment of Psychopathic Personality-Institutional Rating Scale (CAPP-IRS) in a sample of 72 male forensic patients with a primary diagnosis of schizophrenia spectrum disorders. We compared the CAPP-IRS' psychometric properties to those of the Psychopathy Checklist-Revised (PCL-R). The CAPP-IRS showed good interrater reliability and internal consistency except for the CAPP-IRS Cognition and Emotional Domains. There appears to be a larger but intelligible overlap between the CAPP-IRS and schizophrenia symptoms than between the PCL-R and schizophrenia symptoms. Inversely, the PCL-R showed overall stronger associations with risk assessment measures. We conclude that, in (forensic) schizophrenia disorder spectrum patients, the CAPP-IRS has closer associations with clinical features, while the PCL-R is better a predicting risk and life-time dimensions.