Problem A large audit of colonoscopy in the United Kingdom showed that the unadjusted completion rate was 57% when stringent criteria for identifying the caecum were applied. The caecum should be reached 90% of the time. Little information is available on what units or operators need to do to improve to acceptable levels. Design Quality improvement programme using two completed cycles of audit. Setting Endoscopy department in a university linked general hospital in northeast England. Key measures for improvement Colonoscopy completion rate. Strategy for change Two audit cycles were completed between 1999 and 2002. Changes to practice were based on results of audit and took into account the opinions of relevant staff. Lack of time for each colonoscopy, poor bowel preparation, especially in frail patients, and a mismatch between number of colonoscopies done and completion rate for individual operators were responsible for failed colonoscopies. Appropriate changes were made. Effects of change The initial crude colonoscopy completion rate was 60%, improving to 71% after the first round of audit and 88% after the second round, which approximates to the agreed audit standard of 90%. The final adjusted completion rate was 94%. Lessons learnt Achievement of the national targets in a UK general hospital is possible by lengthening appointments, admitting frail patients for bowel preparation to one ward, and allocating colonoscopies to the most successful operators.