The purpose of the present study was to establish an optimal colon preparation for persons with diabetes who are undergoing colonoscopies. Specifically, the aim was to compare the difference between an experimental and standard preparation. Adequacy of bowel preparation is critical for good bowel visualization. Compared with nondiabetic patients, persons with diabetes have slower gastric emptying, colonic transit, and colon evacuation. Inadequate preparations may lead to suboptimal colonoscopy resulting in overlooked pathology, repeated examinations with associated risks, and organizational inefficiencies. Using a single-blind experimental design, 198 persons with diabetes who were scheduled to receive colonoscopies were randomly assigned to either the experimental (diabetic colon preparation) or the control (standard colon preparation) group. Patients in the diabetic colon preparation group had 70% good colon preparations compared with 54% in the standard group, and this finding was significant (χ2 = 5.14, p = 0.02). Results indicate that diabetic patients receiving 10 ounces of magnesium citrate 2 days prior to their colonoscopies followed by 10 ounces of magnesium citrate and 4-L polyethylene glycol the day prior to the procedure had cleaner colons than those receiving standard preparation of 10 ounces of magnesium citrate and 4-L polyethylene glycol the day prior to procedure. This colon preparation is safe, feasible, well-tolerated, and effective.