It is becoming increasingly apparent that genetic research into psychiatric disorders would benefit from consideration of the environment because these risk mechanisms are likely to interact. Despite generalised anxiety disorder (GAD) being one of the most prevalent disorders presented in primary care, there is a paucity of published studies of gene-environment interactions (G x E) for this phenotype. This article describes how our current knowledge of GAD is useful in designing studies of G x E for GAD. To increase the chances of identifying replicable G x E for GAD further information is needed with regards to: defining and measuring GAD, difficulties co-occurring with GAD, quantitative genetic estimations for GAD, specific genes associated with GAD, and specific environmental risks for GAD.