Objective: This primary purpose of this study was to examine cognitive complexity and readability of patient-administered ADHD scales. The secondary purpose was to estimate variation in readability of individual ADHD scale items. Method: Using comprehensive search strategies, we identified eight English-language ADHD scales for inclusion in our study. A complete copy of each ADHD scale was obtained from the most current publication. Cognitive complexity of individual ADHD scale items were assessed using three techniques (number of items, number of words, and linguistic problems), while readability was calculated using the Flesch-Kinkaid formula. Results: Total number of ADHD scale items ranged from 6 to 66. The ADHD scale items averaged from a low of 4.4 [plus or minus] 2.9 to a high of 18.7 [plus or minus] 4.4 words. Most individual ADHD scale items had between 1 to 3 linguistic problems. Although readability of ADHD scales ranged from approximately 5th to 8th grade, there was notable variation in readability across individual statements and questions. Conclusion: Formatting characteristics, including linguistic problems and high readability, may interfere with patients' ability to accurately complete ADHD scales. (Contains 2 figures and 4 tables.)