Flexible endoscopy, performed after oral bowel preparation and under moderate intravenous sedation, proves to be well tolerated, safe and highly effective in the diagnosis and management of children with IBD. At St Bartholomew's Hospital it is performed as the investigation of first choice, on the basis that it supplies colour documentation, histopathological and (where relevant) bacteriological evidence, which achieves certain confirmation or exclusion in almost every case and in the shortest possible time. Biopsies must always be taken, as mucosa of normal appearance can show either microscopic ulcerative colitis or Crohn's disease. When there are the characteristic 'aphthoid' ulcers, visual diagnosis of Crohn's disease is reasonably certain, particularly in early-stage disease, although amoebic and other infective causes of colitis can give misleadingly similar appearances. The endoscopist can usually inspect (and almost always biopsy) the terminal ileum, and can expect many children to show the prominent 'nodular lymphoid hyperplasia' which is essentially a normal finding-though sometimes misdiagnosed radiologically as being Crohn's deformity. However, it is important that radiological assessment by barium follow-through complements colonoscopy in view of the not infrequent cases of intestinal Crohn's disease in children where the proximal small intestine is involved, even if the colon and terminal ileum are spared.