This article presents an American psychometric instrument; the Child Behavior Checklist for Ages 1-5 (CBCL/1-5) appropriate for application in the clinical setting and in research for assessment of behavioural, emotional and social problems in preschool children. Selected scores from a Danish population-based sample and a clinical sample on the CBCL/1-5 and the Caregiver Report Form (C-TRF) are presented. CBCL/1-5 and C-TRF seem reliable and valid for assessing psychopathological problems in preschool children from the perspectives of multiple informants in diverse settings.