Regional enteritis is the older name for Crohn’s disease, a chronic inflammatory bowel disease that can affect any part of the gastrointestinal tract from mouth to anus, though it most often strikes the end of the small intestine and the start of the colon. The inflammation is patchy and transmural, burrowing through the full thickness of the bowel wall, which distinguishes it from ulcerative colitis. Symptoms include abdominal pain, diarrhoea, weight loss, and fatigue, with flare-ups and remissions over a lifetime. Nutrition management is central: exclusive enteral nutrition can induce remission in children, deficiencies of iron, B12, and vitamin D are common, and some patients need to avoid fibre or lactose during flares. The cause remains unknown, with genetics, immune dysfunction, and gut microbes all implicated.