Neuropsychological testing is one method used for diagnosing ADHD across the lifespan. This comprehensive approach incorporates performance-based measures with a detailed history, teacher and parent (and others’) standardized reports, and clinical observations. This chapter walks the reader through neuropsychological testing for the adolescent with suspected ADHD. Through descriptions of measures commonly included in neuropsychological testing, readers will come to understand how tests are chosen and interpreted. Given the high frequency of disorders mimicking or co-occurring with ADHD, we explain the process of disentangling an often complex presentation into an accurate overall profile. Finally, we address recommendations commonly resulting from neuropsychological testing as they relate to specific findings.