Objective: Preparing for a definitive randomized clinical trial (RCT) of neurofeedback (NF) for ADHD, this pilot trial explored feasibility of a double-blind, sham-controlled design and adherence/palatability/relative effect of two versus three treatments/week. Method: Unmedicated 6- to 12-year-olds with "Diagnostic and Statistical Manual of Mental Disorders" (4th ed.; "DSM-IV") ADHD were randomized to active NF versus sham-NF and to 2X versus 3X/week treatment frequency. Frequency switch was allowed after Treatment 24. Results: In two school years, 39 participants were recruited and 34 (87%) completed all 40 treatments. Child/parent guesses about assigned treatment were no better than chance. At Treatment 24, 38% chose 2X/week and 62% chose 3X/week. Both active NF and sham yielded large pre-post improvement on parent ratings but NF no more than sham. Conclusion: Blinding appears to work, and sham does not prevent recruitment/retention. Treatment frequency of 3X/week seems preferred over 2X/week and was as effective. A large double-blind RCT is feasible and necessary to test specific NF effectiveness. (Contains 4 figures and 1 table.)