There has been much interest in the genetics of attention deficit hyperactivity disorder and molecular genetic studies are now underway. The success of genetic studies will depend on how well the phenotype is defined. Twin studies using parent and teacher rated questionnaires or interviews all appear to yield highly heritable measures. Nevertheless, there is evidence to suggest that parent measures are subject to rater bias. Consequently there has been much interest in obtaining more objective measures of related traits such as attention span and impulsiveness using, computerised neuropsychological tasks. However there have been few twin studies examining the genetic contribution to these neuropsychological measures. The present study aims to investigate whether performance on the Matching Familiar Figures Test (MFFT) and Continuous Performance Task (CPT) is genetically influenced in childhood. 20 monozygotic (MZ) and 20 dizygotic (DZ) twin pairs were randomly selected from the Greater Manchester Twin Register. Preliminary data suggest that MZ twins perform more similarly than DZ twins on the MFFT, but not the CPT. Future work needs to examine whether other neuropsychological measures commonly used in research on ADHD are genetically influenced using larger twin samples.