Attention-deficit hyperactivity disorder (ADHD) varies in its clinical presentation and course. Susceptibility gene variants for ADHD and associated antisocial behaviour are being identified with emerging evidence of gene-environment interaction. Genes and environmental factors that influence the origins of disorder are not necessarily the same as those that contribute to its course and outcome. ; PUBLISHED ; We acknowledge funding from the Wellcome Trust (A.T., M.G.) and the Medical Research Council (P.A.). K.L. is supported by a Wellcome Trust Value in People Award.