Children diagnosed with either Crohn's disease (CD) or Ulcerative Colitis (UC) under follow-up at the Pediatric gastroenterology institute, Schneider Children's Hospital, will be enrolled. Patients can be enrolled at diagnosis or at any time point during follow-up. Patients' characteristics will be retrieved from their medical files including demographic details, disease phenotype, anthropometric measures, laboratory evaluation, complication and therapeutic regimens. At enrollment all patients will perform body composition assessment by air displacement plethysmography (ADP) and DEXA (no greater than 7 days between the 2 methods of measurement). At one and two years following initial assessment ADP measurement will be repeated, mid arm circumference and skin fold measurements will be taken and the patient will fill a physical activity questionnaire. Disease activity score (either Pediatric Crohn's Disease Activity Index for CD or Pediatric Ulcerative Colitis Activity Index for UC) will be calculated. Similar evaluation will be performed prior and immediately following exclusive enteral nutrition or corticosteroid courses and prior to any biologic therapy initiation.