Attention deficit hyperactivity disorder (ADHD) is characterised by developmentally inappropriate and impairing levels of inattentive and hyperactive-impulsive behaviours. We aimed to investigate the differential effects of parent and teacher ratings on inattention and hyperactivity-impulsivity and the extent of genetic overlap between the two behavioural dimensions. Multivariate structural equation modelling was performed on DSM-IV based ADHD ratings by parents and teachers collected on a general population sample of 672 twin pairs, at ages 7-10 years. This study is the first to simultaneously use parent and teacher ratings in twin modelling to examine the effects of different raters on the two behavioural dimensions of ADHD. The findings indicated that hyperactivity-impulsivity and inattention load on to separate latent factors that represent a common behavioural view for both parents and teachers, although there are additional aspects to the observations of these behaviours that are unique to each type of rater. The findings further indicate some shared aetiology for hyperactivity-impulsivity and inattention as measured by both parent and teacher ratings, in agreement with previous findings on the aetiology of the two symptom dimensions of ADHD.