Objective: The current study examines psychometric properties of the Weiss Functional Impairment Rating Scale (WFIRS), a measure of adult ADHD-related impairment. It is a self-report questionnaire that provides a metric of overall life impairment and domain-specific dysfunction. Method: Using data from a large (N = 2,093), multi-institution sample of college students and including a subsample of collateral informants (n = 262), a series of analyses were conducted. Results: The WFIRS demonstrated robust internal reliability, cross-informant agreement on par or superior to other measures of ADHD symptomatology and impairment, and concurrent validity. The WFIRS was not shown to be uniquely associated with ADHD, as internalizing symptoms also associated with the total and domain scores. Conclusion: The use of the WFIRS in identifying ADHD-related impairment in emerging adults appears to be psychometrically supported, and will prove useful to clinicians and researchers.