Not all colonoscopies can be completed to the cecum with a standard colonoscope. The utility and sequencing of various available instruments was studied. METHODS: Data was collected prospectively in 3,209 consecutive cases in a referral colonoscopic practice. 3,174 exams were performed with a standard colonoscope (C), with 105 failures (3.3%) Success was reaching the cecum or ileocolic anastomosis. Cases were excluded if luminal obstruction was due to tumor. Immediately after failed colonoscopy, a standard gastroscope (G) was used in 103 cases and in 2 patients, a 225 cm enteroscope (E) was used. E was used in 5 cases as a third instrument, when both C and G failed. In 33 cases, G was used as a primary instrument when there was a history of a prior failed attempt with C; 2 patients had E as a primary exam. RESULTS: When C failed (105 patients), the tip did not pass beyond the sigmoid colon in 79%. Whenever G was used, there was success in 118/140 patients (84%) when C failed. In 22 patients, G failed in 2 because of a sigmoid stricture, no other scope was used in 5 patients. E was successful in 2 patients as a primary scope, and in 2/3 as a secondary scope; in one E only reached the ascending colon. When both C and G failed, E was successful in 5 of 5 attempts. When C failed, an attempt with another C of different flexibility was successful in 2 patients, and in 1 only reached the hepatic flexure C repeat was successful in 2 patients when G and C failed Excluding 2 sigmoid strictures, when additional scopes were used after failure with both C and G, success was achieved in all but 2 attempts If either the C or G was able to pass beyond the sigmoid, success was achieved with an additional long scope in 11 of 12 attempts (8E,3C). If E is not available, another attempt with C is worthwhile (success in 3/3) CONCLUSION: For greater success in colonoscopy, G should be used when C fails C failure is usually due to inability to pass the sigmoid colon. Further success can be achieved with an enteroscope or repeat attempt with C when either C or G is able to pass beyond the sigmoid colon. When obstruction from tumor or stricture was excluded, the use of multiple instruments was successful in 99.4% of cases.