Results from family studies, adoption studies and, in particular, twin studies have indicated that there is a strong genetic predisposition to ADHD. However, environmental factors also appear to be important. No single gene is associated with a high risk of ADHD. Among the candidate genes that have been studied, the increased risk of ADHD associated with each gene is small; it is highest for the dopamine receptor gene DRD4 (odds ratio 1.33, 95%, confidence interval 1.15-1.54). Although genetic studies offer great promise and there have been significant advances in the technology, the translation of genetics research into clinical practice for the management of ADHD remains a challenge.