We performed a systematic review of the literature by a computer search of databases and review of references of all articles retrieved, in particular the references of previous extensive reviews of the topic at hand [15–16, 51, 55, 64]. We searched Medline and PsychInfo from 1987 to October of 2008 for articles written in English, Spanish or Portuguese (the languages of the authors) using the following words; CD, ODD, child and adolescent, prevalence rates, epidemiologic studies, mental disorders and symptoms of CD, ODD. Our search in Medline produced 5,352 abstracts, and in PsychINFO resulted in 2,815 abstracts for a total of 8,209 abstracts. All abstracts were reviewed by the first author and the abstract was selected for review if it met the following criteria: 1) the study presented prevalence rates based on a probability school or community household sample of children 18 years of age or less including population based twin data and birth registers; 2) the prevalence rates were based on DSM-III-R or DSM-IV criteria. If only preschool children were enrolled, the study was excluded. We reviewed 1,237 abstracts
