PURPOSE:During colonoscopy, smooth insertion of the colonoscope is an important basic procedure. However, it is not necessarily easy. An understanding of the passage patterns of the colon is helpful for colonoscopy. In this study, the authors aimed to contribute information that could be useful to effect a smooth and effective introduction of the colonoscope. METHODS:The authors performed 7,560 colonoscopies from May 2000 to December 2000. All cases were performed without using sedatives or analgesics. Out of those 7,560 cases, 2,289 cases, which were performed by one colonoscopist, were selected, excluding those with incomplete colonoscopy, those with a history of bowel resection, those with poor bowel preparation, those with advanced disease, such as inflammatory bowel disease, cancer, etc., and those with conditions that could markedly affect colonoscopy. Those 2,289 cases were classified as 4 patterns according to the passage patterns through the colon during colonoscopy:pattern A, passage is possible using right torque and pull-back; pattern B, bowel-shortening is possible at the peak point of the sigmoid colon; pattern C, bowel-shortening is possible at the transverse colon because of a markedly redundant sigmoid colon; and pattern D, pattern is difficult to specify. Those 2,289 cases were also analyzed regarding age. As to age, they were divided into two groups, those under the 6th decade and those of the 6th decade or older. RESULTS:The most common pattern was pattern A, comprising 71.3%; next was pattern B, 19.7%. There was no significant difference in distribution of the passage patterns between the two age groups (P>0.05). CONCLUSIONS:Ninety-one percent (91%) of the cases were patterns A and B. An understanding of the passage patterns will be helpful for smooth insertion of the colonoscope. The 'axis-maintaining and bowel-shortening method' is a useful and effective approach to colonoscopy.