Objectives: comparison of the effects of computer-assisted cognitive rehabilitation and taking Methylphenidate (Ritalin) on executive functions and clinical symptoms of attention-deficit/ hyperactivity disorder. Design: matched, randomized, no blind design, second experimental group as control. Population: inclusion criteria: ADHD diagnosis; age between 7 and 11; IQ>85. Exclusion criteria: sever co-morbid disorder; seizures; IQ<85; disability; sever medical condition; sample size: total of 34. Interventions: computer assisted cognitive rehabilitation (n=14), taking Methylphenidate (n=20). Assessment: pre-test, post-test, and an one month follow-up; measurement instruments: continuous performance test; wechsler digit span test; span board test; Raven's test; Persian version of tower of London test; Swanson, Nolan, and Pelham scale (to measure ADHD symptom intensity). Time: two months period of intervention for both groups; rehabilitation group received 20 one-hour-sessions of computerized training of executive functions, and drug therapy group simultaneously received 2 to 3 doses of Ritalin per day for two months. Original outcome variables: executive function tasks and the scale of severity of symptoms of attention deficit/ hyperactivity disorder.