Background:  Clinical studies have documented differences in detection rates of colorectal cancers and adenomas between experienced colonoscopists, the basis of which is unknown. The aim of this study was to determine whether colonoscopic withdrawal technique varies between 2 colonoscopists with known differences in adenoma detection rates. Methods:  Ten consecutive colonoscopic withdrawals by each of the 2 colonoscopists were videotaped and then assessed according to specific criteria by 4 experts blinded to who had performed the colonoscopies. Results:  Each of the 4 experts scored the colonoscopist with the lower miss rate significantly higher (p < 0.001) for each of 4 quality criteria: (1) examining the proximal sides of flexures, folds and valves, (2) cleaning and suctioning, (3) adequacy of distention, and (4) adequacy of time spent viewing. Conclusion:  Higher quality colonoscopic withdrawal technique as determined by expert observers was associated with a colonoscopist with a previously documented lower miss rate for adenomas. Colonoscopic withdrawal technique should be subjected to further study and standards for withdrawal technique should be developed. (Gastrointest Endosc 2000;51:33-6.)