Forty children with and 40 children without Attention deficit Hyperactivity Disorder (ADHD) receive Docosahexaenoic Acid (DHA) and Eicosapentaenoic Acid (EPA) or placebo via a dietary intervention. Cognitive control functions are measured with functional Magnetic Resonance Imaging (MRI) before and after the intervention. Behavioural change is monitored with behavioural scales.

Inclusion Criteria:

Inclusion criteria for subjects with ADHD

1. 8-12 year old boys
2. Diagnostic and Statistical Manual 4th edition (DSM-IV (APA, 1994)) diagnosis of ADHD, according to Diagnostic Interview Schedule for Children (DISC)
3. Scores in the clinical range on the Child Behaviour Checklist (CBCL) and Teacher Rating Form(TRF)
4. Ability to speak and comprehend Dutch.
5. Used to daily consumption of margarine

Inclusion criteria for controls

1. 8-12 year old boys
2. No DSM-IV (APA, 1994) diagnosis, according to DISC interview
3. No scores in the clinical range on the Child Behaviour Checklist (CBCL) and Teacher Rating Form (TRF)
4. Ability to speak and comprehend Dutch. 5 Used to daily consumption of margarine

Exclusion Criteria:

1. mental retardation (IQ < 70)
2. major illness of the cardiovascular, the endocrine, the pulmonary or the gastrointestinal system
3. presence of metal objects in or around the body (pacemaker, dental braces)
4. history of or present neurological disorder
5. regular use of n-3 or n-6 fatty acid dietary supplements, products fortified with EPA or DHA, a regular diet high in fatty fish (= 1 serving per week) or participation in intervention studies or (school-) health programs in the four months prior to study participation.