The purpose of this study was to analyze and compare diagnoses of patients from a special outpatient department for infants, toddlers and preschoolers. Specifically, overlap, age and gender differences according to the two classification systems DC: 0-3R and ICD-10 were examined. 299 consecutive children aged 0-5;11 years received both ICD-10 and DC: 0-3R diagnoses. All ICD-10 diagnoses were given prospectively at the initial contact. The DC: 0-3R diagnoses were allotted in mutual consensus conferences. The most common ICD-10 disorders were Oppositional Defiant (ODD), Hyperkinetic (HKD) and Emotional Disorders. In DC: 0-3R, nearly half of the children could not be coded adequately ("Other Disorders"). Sleep Behavior Disorders were followed by Feeding Behavior and Regulation Disorders. Both classification systems are needed in infant, toddler and preschool psychiatry. There is a good concordance of the two systems for Feeding, Sleeping, Adjustment and Attachment Disorders, whereas the ICD-10 diagnoses HKD and ODD are not adequately represented in DC: 0-3R.