Reassurance seeking (RS) is a common though understudied behavior in numerous mental disorders including obsessive-compulsive disorder (OCD), depression, and anxiety disorders. Research suggests that individuals with different mental disorders may seek reassurance about similar concerns, namely perceived relational/social threats (e.g., whether one is truly loved) and perceived general threats (e.g., whether the stove is truly off). Additionally, individuals presenting for treatment often have comorbid mental disorders. However, existing measures of RS tend to be disorder-specific and emphasize one focal concern. Further, research as well as anecdotal reports from clients suggest that asking direct questions is only one form of RS, and that individuals commonly use other, more covert/subtle forms of RS as well. Nevertheless, existing measures of RS tend to focus on either social/relational or general threat-related RS, and tend to neglect assessment of covert RS. The Covert and Overt Reassurance Seeking Inventory (CORSI) was developed in response to the perceived need for a comprehensive, transdiagnostic measure of problematic RS to assess covert and overt RS motivated by perceived general and/or relational threats. The CORSI is comprised of 26 items and was found to have a robust 5-factor structure based on exploratory (n = 813) and confirmatory (n = 813) factor analyses previously conducted with large non-clinical samples. The five factors represent Relational Overt (RO), Relational Covert (RC), General-threat Overt (GO), General-threat Covert Active (GCA), and General-threat Covert Passive (GCP) RS behavior. This study presents validity and normative clinical data analyses from samples of individuals meeting diagnostic criteria for OCD (n = 50), depression (n = 30), or an anxiety disorder (n = 60). Participants completed a diagnostic interview and existing measures of clinical symptomatology. Results demonstrated significant differences in CORSI total and factor scores between clinical and non-clinical groups, with all three clinical groups showing significantly higher total scores (t's > 2.01, ps .< .001). When collapsing across the clinical sample, results suggest that the CORSI correlates positively and strongly with existing measures of depression (r = .201, p = .017), anxiety (r = .364, p < .001), and OCD (r = .444, p < .001). Results will be discussed in terms of cognitive-behavioral assessment of and interventions for problematic RS behavior across mental disorders.