Colonoscopy without prior preparation in mild to moderate active ulcerative colitis. We evaluated the effect of different types of preparations on the diagnostic yield of colonoscopy (total or limited) in mild to moderate active ulcerative colitis. Our ability to determine the extent of disease and see the mucosa beyond the inflamed areas was assessed in patients receiving no preparation (group A, 72 examinations) and those receiving diphosphosoda enemas (group B, 181 examinations). There were three failures in group A and 11 in group B. In the majority of patients (71% of group A, 83% of group B) the scope could be passed under optimal viewing conditions at least one segment beyond the involved area. In group A the cecum was reached in 16% of the procedures and in group B in 18%. We conclude that in mild to moderate active ulcerative colitis, colonoscopy can be performed without preparation, and still achieve the same results as with preparatory enemas. 