The objective of this study is to determine the optimal withdrawal time for colonoscopy. A 6-minute withdrawal time is currently the standard of care but has only been evaluated in an observational fashion. The investigators believe that this should be validated in a standardized fashion. If the benefits of a 6 minute withdrawal are proven in this study (ie a low polyp/adenoma miss rate and a high polyp/adenoma detection rate), then this will support widespread adoption of a 6 minute withdrawal as the standard of care. This in turn may decrease the occurence of 'interval colon cancers', which are early colon cancers arising in subjects despite their having undergone colonoscopy. Our hypothesis is that the polyp/adenoma detection rate will be unacceptably low and the polyp/adenoma miss rate will be unacceptably high in the 3-minute withdrawal group when compared to the 6-minute withdrawal group.

Eligible patients will be randomized to colonoscopy with either a 6-minute withdrawal time or a 3-minute withdrawal time. Patients will then undergo colonoscopy. All colonoscopies will be performed by a GI attending (standard of care). The colonoscopy is typically performed under conscious sedation using medications such as fentanyl and midazolam for comfort (standard of care). Occasional patients undergo colonoscopy under general anesthesia. For all patients, advancement of the colonoscope to the cecum will be followed by segmental withdrawal of the colonoscope in each of 3 segments of the examined colon (right side of colon, transverse colon and left side of colon). Following examination of each individual segment, the colonoscope will be readvanced to the proximal end of the segment and a 2 minute withdrawal will be re-performed. For those randomized to the 6-minute withdrawal each segment will be examined over 2 minutes, followed by a "second look" over each segment over 2 minutes by the same endoscopist. For those randomized to the 3-minute withdrawal time, advancement to the cecum will also be followed by segmental withdrawal in each of 3 segments of the examined colon. Each segment will be examined over 1 minute, followed by a "second look" over each segment over 2 minutes by the same endoscopist. All patients will therefore undergo a second look colonoscopy with a 6-minute withdrawal time ('de-facto' standard of care). Polyp/adenoma detection and miss rates will then be calculated and compared between the two groups.

Inclusion Criteria:

• Age > 18
• Already scheduled for colonoscopy

Exclusion Criteria:

• Age < 18
• Pregnant women
• Mentally disabled
• Decisionally challenged
• Cancer subjects
• Healthy volunteers
• Prisoners