Ulcerative colitis (UC) and Crohn's disease together constitute inflammatory bowel disease (IBD). The prevalence of UC is about 30-100 per 100,000 and 30-50 per 100,000 for Crohn's disease. They characteristically present in young adults, but may present at any time of life, including childhood and old age, and a second peak of incidence is now recognised in the sixth decade of life. UC always affects the rectum and then progresses to a variable extent around the colon, but never extends into the small bowel. By contrast, Crohn's disease may occur anywhere in the GI tract, from the mouth to the anus, with skip lesions - inflamed areas affected by Crohn's disease - separated by areas of apparently normal mucosa. The ileocaecal region is the most common site. Crohn's also frequently affects the colon, and can diffusely affect the small bowel. It rarely occurs in the oesophagus, stomach and duodenum. It is important that GPs have a high index of suspicion of IBD and initiate appropriate treatment for patients undergoing relapse of the disease. GPs also have a vital role in the monitoring of patients, often in collaboration with gastroenterologists, particularly for those patients on immunosuppressant therapy.