Cognitive disengagement syndrome (CDS), formerly termed sluggish cognitive tempo, is a set of symptoms characterized by excessive daydreaming, mental confusion, and slowed behavior/thinking. CDS is distinct from symptoms of attention-deficit/hyperactivity disorder (ADHD) and other psychopathologies and uniquely associated with functional impairment. However, despite significant progress in developing and evaluating rating scale measures of CDS, no clinical interview of CDS exists with established psychometric properties that can facilitate a multimethod approach assessing CDS. Accordingly, the present study evaluated the psychometric properties of the semistructured Cognitive Disengagement Syndrome–Clinical Interview (CDS-CI). The CDS-CI and the ADHD inattention (ADHD-IN) and hyperactive-impulsivity (ADHD-HI) modules from the Kiddie Schedule of Affective Disorders and Schizophrenia for School-Age Children (K-SADS) were administered to a sample of early adolescents (N = 341, ages 10–12 years) and their caregivers. Adolescents and caregivers also completed rating scale measures of CDS and ADHD symptoms. The CDS-CI demonstrated high internal consistency and interrater reliability. CDS-CI scores showed excellent same-source discriminant validity from K-SADS, ADHD-IN, and ADHD-HI scores and encouraging convergent and discriminant validity with rating scale measures, especially for caregivers. Above and beyond K-SADS, ADHD-IN, and ADHD-HI scores, higher parent and adolescent CDS-CI scores were both significantly associated with greater functional impairment. A threshold of ≥ 6 out of 15 symptoms was selected as an initial threshold for determining clinically elevated CDS using the CDS-CI. Findings provide psychometric support for the CDS-CI as a tool in the multimethod assessment of CDS.