The purpose of this study was to develop an instrument (Test for Body Image Distortion in Children and Adolescents, BID-CA) suitable for adolescents to detect and quantify body image distortion. Participants were patients with anorexia nervosa (AN; N=75), healthy age-matched control participants (N=268) and age-matched thin female athletes (N=50) with a mean age of 15.2 (standard deviation =2.0) years. We assessed body image distortion (arm, waist, and thigh) using the BID-CA and two scales of the Eating Disorder Inventory-2 (EDI-2; Drive for Thinness, Body Dissatisfaction). Diagnostic validity of the BIDCA was analyzed with receiver operating characteristic (ROC) curves. Additional regression analyses revealed the variables BID-CA thigh and EDI-2 Drive for Thinness to be the best at predicting body image distortion among AN patients. In conclusion, the BID-CA showed good diagnostic validity. It is efficient, language independent, time-saving and seems appropriate for children and adolescents.