Is ADHD a valid disorder in children with intellectual delays?

To assess the validity of ADHD in children with mental retardation, we applied Robins and Guze's [Robins, E., and Guze, S.B. (1970). Establishment of diagnostic validity in psychiatric illness: Its application to schizophrenia. American Journal of Psychiatry, 126, 983-987.] criteria for determining the validity of a psychiatric disorder. We review the literature describing clinical correlates, family history, treatment response, laboratory studies, course, and outcome of children with ADHD and mental retardation. Although clearly an area in need of further research, there is preliminary evidence to suggest that ADHD is a valid psychiatric condition in children with mental retardation. Nevertheless, without knowing the base rates of ADHD symptoms in the mental retardation population, the positive predictive power and negative predictive power of ADHD symptoms in this population remain an open question. In addition to assessment of base rate symptoms, future research should consider what diagnostic algorithm may best be applied to the diagnosis of ADHD in mental retardation.