With the exception of pervasive developmental disorders, there has been considerable controversy about the validity of diagnosis of mental disorders in very young children (ages 2 to 5 years). There is accumulating evidence, however, that mental disorders generally identified in school-age children are quite prevalent in preschool children. In a summary of the community surveys of young children, Logger and colleagues98 reported the following range of rates of childhood disorders: ADHD from 2% to 5.7%; ODD from 4% to 16.8%; CD from 0% to 4.6%; depression from 0% to 2.1 %; and anxiety disorders from 0.3% up to 9.4%. In addition to the prevalence of these disorders in young children, rates of impairment are very high (ie, about 84.6% of those with emotional disorders and 100% of those with behavioral disorders). There is also a high degree of comorbidity in young children with mental disorders; of those with one disorder, approximately 25% have a second disorder. The proportion of children with comorbidity increases about 1.6 times for each additional year from age 2 (18.2%) to 5 (49.7%).98
