1. Relapses For each participant, the number of relapses during the study period will be recorded. For patients with Crohn's disease, a relapse will be defined as an aPCDAI of >15. The PCDAI was originally developed and validated in several centres (18) and has been used widely in paediatric clinical trials. The original PCDAI includes three history items (abdominal pain, number of liquid stools, general wellbeing), five physical examination items (abdominal examination, perirectal disease, extraintestinal manifestations, weight, height velocity), and three laboratory tests (hematocrit, albumin, erythrocyte sedimentation rate). Among other things, the original PCDAI has been criticized because of the inclusion of blood tests. Recent studies have shown that an abbreviated version of the PCDAI (aPCDAI) which omits laboratory items is accurate and predicted disease activity as well as the original PCDAI (12,19). The aPCDAI consists of the three history items (abdominal pain, number of liquid stools, and general well-being), and the three physical examination items (weight loss, abdominal examination, and perirectal disease) of the original PCDAI. In order to avoid repeated blood sampling for research purposes, we will use the aPCDAI (Appendix II). Items in this index are scored on a three-point scale (zero, 5, or 10 points) and scores range from zero to 60 with higher scores indicating more active disease.