BACKGROUND: Brain tissue is selectively enriched with highly unsaturated fatty acids (FAs). Altering the maternal FA status in pregnancy may improve fetal neural development with lasting consequences for child development. OBJECTIVE: We explored whether maternal FAs in erythrocytes, either measured directly or indirectly by maternal FADS genetic variants, are associated with child intelligence quotient (IQ). DESIGN: Linear regression analyses, adjusted for 18 confounders, were used to investigate the associations in 2839 mother-child pairs from the population-based Avon Longitudinal Study of Parents and Children cohort. RESULTS: Low levels of arachidonic acid (20:4n-6) were associated with lower performance IQ (-2.0 points; 95% CI: -3.5, -0.6 points; P = 0.007, increased R(2) = 0.27%), high levels of osbond acid (22:5n-6) were associated with verbal IQ (-1.8 points; 95% CI: -3.2, -0.4 points; P = 0.014, R(2) = 0.20%), and high levels of adrenic acid (22:4n-6) were associated with verbal IQ (-1.7 points; 95% CI:-3.1, -0.3 points; P = 0.016, R(2) = 0.19%). There was some evidence to support a negative association of low docosahexaenoic acid (DHA; 22:6n-3) with full-scale IQ (R(2) = 0.15%). Novel weak associations were also observed for low levels of osbond acid (R(2) ≤ 0.29%) and FADS variants with opposite effects for intron variants and variants in the promoter region such as rs3834458 (R(2) ≤ 0.38%). CONCLUSIONS: These results support the positive role of maternal arachidonic acid and DHA on fetal neural development, although the effects on child IQ by 8 y of age were small (0.1 SD), with other factors contributing more substantially. The endogenous synthesis of these FAs by FADS genes, especially FADS2, may also be important. The replication of these results is recommended.