Objective: This research evaluates effects of vestibular stimulation by Comprehensive Motion Apparatus (CMA) in ADHD. Method: Children ages 6 to 12 (48 boys, 5 girls) with ADHD were randomized to thrice-weekly 30-min treatments for 12 weeks with CMA, stimulating otoliths and semicircular canals, or a single-blind control of equal duration and intensity, each treatment followed by a 20-min typing tutorial. Results: In intent-to-treat analysis (n = 50), primary outcome improved significantly in both groups (p = 0.0001, d = 1.09 to 1.30), but treatment difference not significant (p = 0.7). Control children regressed by follow-up (difference p = 0.034, d = 0.65), but overall difference was not significant (p = 0.13, d = 0.47). No measure showed significant treatment differences at treatment end, but one did at follow-up. Children with IQ-achievement discrepancy less than or equal to 1 SD showed significantly more CMA advantage on three measures. Conclusion: This study illustrates the importance of a credible control condition of equal duration and intensity in trials of novel treatments. CMA treatment cannot be recommended for combined-type ADHD without learning disorder. (Contains 3 tables and 2 figures.)