Plasma and red blood cell n3 fatty acids correlate positively with the WISC-R verbal and full-scale intelligence quotients and inversely with Conner's parent-rated ADHD index t-scores in children with high functioning autism and Asperger's syndrome

•Plasma and red blood cell fatty acid profile and relationships between fatty acids, and cognitive ability and behavioural problems were investigated in ethnically homogenous polish children with Asperger's syndrome/high functioning autism.•Verbal, performance and full-scale IQs correlated positively with plasma and red blood phosphatidylcholine and red blood cell phosphatidylethanolamine n3 docospentaenoic acid (n3DPA, 22:5n3).•Plasma phosphatidylcholine and red blood cell phosphatidylethanolamine eicosapentaenoic (EPA, 20:5n3) and docosahexaenoic (DHA, 22:6n3) acids correlated negatively with behavioural problems (ADHD index and oppositional).•Red blood cell phosphatidylcholine DHGLA (20:3n6), arachidonic acid (AA, 20:4n6), n6 docosatetraenoic acid (22:4n6) and n6 docospentaenoic acid (22:5n6) correlated positively with oppositional, hyperactivity, ADHD index and inattention, and ADHD index, respectively. Findings of the fatty acid status of people with autism spectrum disorders have been incongruent perhaps because of the diversity of the condition. A cross-sectional design study was used to investigated fatty acid levels and relationships between fatty acids, and cognition and behaviour in a homogenous group of children with autism spectrum disorder. Children with Asperger's syndrome (AS) /high functioning autism (n = 44) and healthy siblings (n = 17) were recruited from the Diagnostic and Therapeutic Centre for Children with Autism, Warsaw, Poland. In the AS group, plasma phosphatidylcholine 22:5n3 correlated positively with verbal (r = 0.357, p = 0.019) and full scale (r = 0.402, p = 0.008) IQs, red blood cell phosphatidylcholine 22:5n3 with verbal (r = 0.308, p = 0.044), performance (r = 0.304, p = 0.047) and full scale (r = 0.388, p = 0.011) IQs and red blood cell phosphatidylethanolamine 22:5n3 with verbal (r = 0.390, p = 0.010) and full scale (r = 0.370, p = 0.016) IQs. Whilst, plasma phosphatidycholine 20:5n3 (r = -0.395, p = 0.009), 22:6n3 (r = -0.402, p = 0.007) and total n3 fatty acids (r = -425, p = 0.005), red blood cell phosphatidlycholine 20:5n3 (r = -0.321, p = 0.036) and red blood cell phosphatidylethanolamine 20:5n3 (r = -0.317, p = 0.038), 22:6n3 (r = -0.297, p = 0.05) and total n3 fatty acids (r = -0.306, p = 0.046) correlated inversly with ADHD index. Similarly, inattention was negatively related with plasma phosphatidylcholine 22:6n3 (r = -0.335, p = 0.028), and total n3 fatty acids (r = -0.340, p = 0.026), oppositional with plasm