The development of rating scales for attention-deficit/hyperactivity disorder (ADHD) has traditionally focused on parent-or teacher-rated scales. However, clinician-based instruments are valuable tools for assessing ADHD symptom severity. The ADHD Rating Scale IV (ADHD RS), clinician administered and scored, has been validated as a useful instrument to assess ADHD symptoms among American children and adolescents. In this study, we assessed the psychometric properties of the scale in a recent clinical trial conducted mainly in Europe with over 600 children and adolescents diagnosed with ADHD. The trial was conducted in 11 European countries plus Australia, Israel, and South Africa. Results based on data in the study indicate that this version of the scale has acceptable psychometric properties including inter-rater reliability, test-retest reliability, internal consistency, factor structure, convergent and divergent validity, discriminant validity, and responsiveness. There were low-to-moderate ceiling and floor effects. The psychometric properties were comparable with other validated scales for assessing ADHD symptom severity. These results were consistent across the 14 countries participating in this trial. Overall, the data from this study support the use of the ADHD RS as a clinician-rated instrument for assessing the severity of ADHD symptoms in children and adolescents in Europe.