For a study from 2003 to 2019, researchers looked for individuals with persistent constipation who had anorectal manometry and at least 1 colonoscopy at 2 tertiary referral hospitals. They also found a subset of individuals who had colonic transit tests done using radiopaque markers. Using univariate and multivariate analyses, they discovered demographic, medical, and constipation-related characteristics associated with poor bowel preparation and their impact on standardized quality indicators. Anorectal manometry testing was performed on 274 participants with chronic constipation. Suboptimal bowel preparation was linked to outlet dysfunction (prolonged balloon expulsion) and slow-transit constipation. Outlet dysfunction was also linked to lower cecal intubation rates, adenoma detection, and the detection of sessile serrated polyps. Outlet dysfunction was linked to nearly 3-fold odds of suboptimal bowel preparation [odds ratio (OR): 2.9; 95% CI: 1.6-5.1] and a 3-fold reduction in cecal intubation rates in multivariable analyses controlling for demographics and known factors associated with poor bowel preparation (OR: 0.3; 95% CI: 0.1-0.8). Slow-transit constipation was linked to a greater than 2-fold increased risk of poor bowel preparation among those with radiopaque marker colonic transit tests (OR: 2.2; 95% CI: 1.1-4.4). Outlet dysfunction was linked to inadequate bowel preparation and other quality measures in a group of individuals with chronic constipation who had a colonoscopy. Patients with constipation and a rectal evacuation issue may be a subgroup of patients who would benefit from personalized bowel preparation procedures.