Awareness of children with significant problems in intellectual development can be traced to antiquity but awareness of associated problems in mental health is a much more recent phenomenon. The increase in awareness in recent years can be related to several factors: greater inclusion of individuals with disabilities in the population, the need to support individuals of all ages in their communities, and increasing sophistication on the part of both researchers and clinicians. Sadly, and somewhat paradoxically, a diagnosis of intellectual disability in the more distant past often led to a presumption that such individuals were somehow protected from other problems – the phenomenon known as ‘diagnostic overshadowing’. However, research with this population began to suggest that rather the converse was true, with persons exhibiting milder intellectual disability having 4- to 5-fold increases in rates of associated psychiatric problems (Reiss & Szyszko, 1983). Awareness also began to increase regarding the difficulty of applying the usual models of psychiatric nosology, particularly in individuals with more severe intellectual disability (Fletcher et al, 2007).Other work began to note significant associations between certain syndromic forms of intellectual disability and specific mental disorders (Dykens & Hodapp, 2001). This volume provides an important overview and update of the current status of the field, and areas where more work is needed.

The opening chapters of this book provide a very helpful overview of basic issues and approaches to classifying intellectual disability and characterising behavioural phenotypes. The next section summarises comorbidity, with specific chapters on commonly associated conditions in general, and anxiety disorders in particular. Relevant disorders are highlighted including behavioural difficulties, problems associated with seizure disorders, and pharmacological management.

Part three of the volume focuses on autism and related conditions. This is an area where there has been a vast increase in research, although, unfortunately, problems in adolescents and adults have been much less frequently addressed. Chapter 8 provides a helpful overview, with other chapters focused more specifically on Asperger syndrome and on pharmacological management.