ABSTRACT
ADHD rarely exists as a single disorder and coexistence or comorbidity is very common ( Jensen et al. 1997; Dalsgaard et al. 2002; Gillberg et al. 2004;
Hurtig 2007). Indeed, as many as two-thirds of children and young people with ADHD will have one or more other mental health, neuropsychiatric or developmental disorders (Kaplan et al. 2001; Green et al. 2005). Some have gone as far to say that ADHD without additional comobidity is rare and may not exist at all (Salmon et al. 2006). This means that the process of assessment is rarely straightforward and can often be complex. In particular, the interpretation of hyperactivity can be difficult and treatment decisions may sometimes be controversial. This is both in terms of the high potential for differential diagnosis, and the risks of over-and underdiagnosis of ADHD.
