The study compares the efficacy of methylphenidate, dextroamphetamine and placebo on neuropsychological functioning and behavioral symptoms in 36 children diagnosed with ADHD within a double-blind cross-over design over six weeks. The assessment of ADHD followed formalized guidelines and a diagnosis of ADHD was based on DSM-IV criteria. A neuropsychological testbattery and four behavioral questionnaires were selected as efficacy variables. The neuropsychological testbattery includes Qb-test (visual attention, inhibitory control, motor activity), Score (auditory attention), Stroop Test (processing speed, inhibitory control) and Grooved Pegboard (motor speed). The participants were tested once on each type of medication. The four questionnaires are: a)Side-Effects Rating Scale (completed by a parent at the end of each of the six weeks), b)Self-Report Questionnaire (completed by the child at the end of each of the six weeks), c)Parent and Teacher Questionnaire(completed by a parent and a teacher Monday till Friday through every week), Test Performance Questionnaire (completed by the child immediately after each of the three test sessions).

Main hypothesis: A trial including both dextroamphetamine(Dex) and methylphenidate(Met) will provide better results than a trial including only Met. a)Met and Dex are efficient as treatment for ADHD compared to placebo, albeit Dex has moderately better effect compared to Met. b)At an individual level some of the participants will show positive response to one type of stimulants and no response, mixed response or adverse response to the other type of stimulant. c)Neuropsychological tests and behavioral questionnaires are moderately in agreement but also add unique information in the assessment of the effect of stimulants. d)Qb-test is sensitive and valid as a measure of the effect of stimulants.

Inclusion Criteria:

• Age from 9.0 to 14.0.
• ADHD diagnosis following assessment at a child & adolescent outpatient clinic.
• Clarification for stimulant treatment.

Exclusion Criteria:

• Moderate or severe mental retardation.
• Psychosis.
• Proven brain damage.
• Sensory deficits and/or motor impairments that make the individual in question unsuitable for the relevant tests.
• Epilepsy.
• The child has previously been prescribed stimulant medication or is being treated with such medication.
• The child commutes between parents or there are other factors that substantially reduce the possibility of obtaining reliable observations from parents (The child needs to live in one place through out the whole trial since otherwise might severely influence the child's behaviour and the observations).