This thesis focuses on the early detection by Dutch Preventive Child Healthcare (PHC) of children with psychosocial problems and especially on the question whether short questionnaires can improve this early detection. The following questions were answered: 1. Can differences in the number of children identified as having psychosocial problems by individual health professionals be explained by differences in the prevalence of problems or background characteristics in the groups of children they examine? 2. What are the psychometric qualities of a number of short questionnaires PCH could use to identify children with psychosocial problems and could they improve the identification by PCH? 3. Is it possible to develop a Computerized Adaptive Test, using items from questionnaires on psychosocial problems and could they improve the identification by PCH? In accordance with the conclusion of an expert meeting in 1999 on the prevention of psychosocial problems among children and adolescents by PCH, the term psychosocial problems will be used in this thesis to indicate emotional and behavior problems and problems at school.