AbstractBackgroundThere is a need to develop a multipurpose obsessive–compulsive disorder (OCD) measure that is useful for cross disorder research and as a reliable clinical rating scale. The current study examined the psychometric properties and established clinical cutoffs for the parent‐report version of the Toronto Obsessive–Compulsive Scale (TOCS), a 21‐item rating scale of obsessive–compulsive traits.MethodParticipants ranged in age from 6 to 21 years old and had a primary diagnosis of OCD (n= 350, 50% female), attention‐deficit/hyperactivity disorder (ADHD) (n= 820, 25% female), autism spectrum disorder (ASD) (n= 794, 22% female), or were typically developing controls (n= 391, 51% female). Confirmatory factor analyses, internal consistency reliability, and convergent and divergent validity of the TOCS were examined in the OCD group. Using various scoring approaches, receiver operating characteristic (ROC) analyses were used to establish a clinical cut‐off by splitting the OCD group into a discovery sample (166 OCD cases, 164 controls) and a validation sample (184 OCD cases, 227 controls). Classification accuracy and TOCS scores were compared across OCD, ADHD, and ASD groups.ResultsThe psychometric properties of the TOCS were confirmed. ROC analyses across TOCS scoring approaches in the discovery sample indicated excellent diagnostic discrimination (AUC ≥0.95, sensitivity 77%–92%, specificity 92%–98%). Established cutoffs, when applied in the independent validation sample of OCD cases and controls, showed an overall classification accuracy of 85%–90%. The TOCS total score and symptom count showed good discrimination of OCD from ADHD (AUC ≥0.86) and ASD (AUC ≥0.81). The OCD group scored significantly higher on all TOCS dimensions (except Hoarding) than the ADHD and ASD groups.ConclusionThe TOCS is a reliable and valid rating scale with strong sensitivity and specificity in discriminating OCD cases from controls, as well as from ASD and ADHD. It is a quantitative OCD measure with important clinical and research applications, with particular relevance for cross disorder phenotyping and population‐based studies.