ADHD is a common disorder which affects around 5% of school aged children and can cause difficulties for individuals in academic, social and family situations. Not all individuals with ADHD have the same profile of problems and long term outcome. For example, some have additional problems such as antisocial behaviour, autistic traits and anxiety or depression. Some individuals grow out of their ADHD, whilst others continue to have problems in adolescence and adulthood. Identifying those individuals who have additional problems is important for monitoring and potential intervention. Sleep problems are known to be common in children with ADHD traits and diagnoses and can be especially impairing for individuals and their families. Whilst there is some evidence to suggest that sleep problems are associated with increased risk of additional problems in ADHD, much more work is needed to understand the relationship between sleep problems and these problems, especially as children grow into adolescence. We want to test the proposal that sleep problems in children with ADHD are an index of severity. Assessing sleep problems in children with ADHD will help identify a more severely affected sub-group at increased risk of poorer outcomes in later adolescence.