Suboptimal omega-3 polyunsaturated fatty acid (n-3 PUFA) levels may contribute to attention deficit hyperactivity disorder (ADHD) and related developmental problems. Associations between n-3 and omega-6 (n-6) PUFA levels in red blood cells (erythrocytes) and learning and behaviour were investigated in 75 children aged 7-12 with ADHD. Children provided blood samples and underwent cognitive assessments. Parents completed questionnaires and Conners' Rating Scales. Controlling for covariates, higher n-3 PUFA predicted lower anxiety/shyness (β = -.27), higher docosahexaenoic acid (DHA) better word reading (β = .22), and higher n-6 PUFA poorer reading (β = -.34), vocabulary (β = .-.26), spelling (β = -.30) and attention (β = -.30). Thirty-six per cent of the sample with learning difficulties had lower DHA than those without (M = 3.26 ± 0.54 vs M = 3.68 ± 0.76, p = .02). This study is the first to compare erythrocyte PUFAs (a measure of PUFA status) in children who have ADHD with and without learning difficulties, and supports emerging indications that the former may be more likely responders to n-3 PUFAs.