Omega-3 fatty acids are dietary essentials, and are critical to brain development and function. Increasing evidence suggests that a relative lack of omega-3 may contribute to many psychiatric and neurodevelopmental disorders. This review focuses on the possible role of omega-3 in attention-deficit/hyperactivity disorder (ADHD) and related childhood developmental disorders, evaluating the existing evidence from both research and clinical perspectives. Theory and experimental evidence support a role for omega-3 in ADHD, dyslexia, developmental coordination disorder (DCD) and autism. Results from controlled treatment trials are mixed, but the few studies in this area have involved different populations and treatment formulations. Dietary supplementation with fish oils (providing EPA and DHA) appears to alleviate ADHD-related symptoms in at least some children, and one study of DCD children also found benefits for academic achievement. Larger trials are now needed to confirm these findings, and to establish the specificity and durability of any treatment effects as well as optimal formulations and dosages. Omega-3 is not supported by current evidence as a primary treatment for ADHD or related conditions, but further research in this area is clearly warranted. Given their relative safety and general health benefits, omega-3 fatty acids offer a promising complementary approach to standard treatments.