Objective: The current study sought to establish psychometric properties of the ADHD-FX (a culturally sensitive measure designed to assess functional impairment related to ADHD) in a dual-site clinical sample. Method: We analyzed patient charts of 67 children (47 boys and 20 girls, ages 5 to 15 years) receiving comprehensive assessments from two university-based ADHD clinics. Results: The parent and teacher ADHD-FX rating scales demonstrated good psychometric properties via adequate reliability (Cronbach’s α > .70), convergent construct validity (significant correlations with majority of theoretically related measures), and divergent construct validity (insignificant correlations with majority of theoretically unrelated measures). Conclusion: Results extend upon previously published psychometric analyses to suggest that the ADHD-FX is a reliable and valid measure for parents and teachers to assess functional impairment related to ADHD (i.e., difficulties with academic achievement, social competence, and familial relationships) in community and clinical populations. Clinical implications and future directions are discussed.