Diagnostic accuracy of the Diagnostic and Statistical Manual of Mental Disorders-oriented Child and Adolescent Symptom Inventory (CASI-4R) Psychotic Symptoms scale was tested using receiver operating characteristic analyses to identify clinically significant psychotic symptoms. Participants were new outpatients (N = 700), ages 6.0 to 12.9 years (M = 9.7, SD = 1.8) at 9 child outpatient mental health clinics, who participated in the Longitudinal Assessment of Manic Symptoms (LAMS) Study baseline assessment. Because LAMS undersampled participants with low mania scores by design, present analyses weighted low scorers to produce unbiased estimates. Psychotic symptoms, operationally defined as a score of 3 or more for hallucinations or 4 or more for delusions based on the Schedule for Affective Disorders and Schizophrenia (K-SADS) psychosis items, occurred in 7% of youth. K-SADS diagnoses for those identified with psychotic symptoms above threshold included major depressive disorder, bipolar spectrum disorder, attention deficit/hyperactivity disorder, posttraumatic stress disorder, psychotic disorders, and autism spectrum disorder. The optimal psychosis screening cut score (maximizing sensitivity and specificity) was 2.75+ (corresponding diagnostic likelihood ratio [DiLR] = 4.29) for the parent version and 3.50+ (DiLR = 5.67) for the teacher version. The Area under the Curve for parent and teacher report was .83 and .74 (both p < .001). Parent report performed significantly better than teacher report for identifying psychotic symptoms above threshold (p = .03). The CASI-4R Psychosis subscale (J) appears clinically useful for identifying psychotic symptoms in children because of its brevity and accuracy.