There are many factors that influence successful outcomes in colonoscopy. The aims of this study were to evaluate these factors and determine ways to improve outcomes. All participants (N = 229) who underwent planned colonoscopy between July and September 2004 were retrospectively included. Participants included 118 men and 111 women with a mean age of 59 years. Completion rate was 92%. Reasons of failure included poor bowel preparation (2.2%, p < .025), bowel looping (2.2%, p < .025), participant discomfort (1.3%), and obstructing lesion (1.3%). Mean midazolam dose was 3.8 mg. Three participants (1.3%) had midazolam alone, and all had complete colonoscopy. One hundred thirty-three participants (60.7%) had additional meperidine, with a completion rate of 94%. Eighty three participants (37.9%) had additional meperidine and Buscopan®, with a completion rate reduced to 89.2%. There was no correlation between sedatives used and completion rate. Completion rate of colonoscopy in our unit was acceptable at 92%. A combination of midazolam and meperidine gave the best completion rates (94%). The two main reasons for incompletion were poor bowel preparation and excessive bowel looping.