The deterioration of three patients with ulcerative colitis shortly following colonoscopy made us question whether this was related to the colonoscopy or bowel preparation, this trial was set up to answer this question. A total of 105 patients were recruited and underwent full bowel preparation and colonoscopy. Results showed that there was no statistically significant difference between patients with ulcerative colitis and controls with non-inflammatory disease in increase in bowel frequency, general well being or pain. In summary we conclude that full bowel preparation and colonoscopy in patients with ulcerative colitis managed as outpatients do not lead to a deterioration in their symptoms.