Recommendations regarding optimal bowel preparation for fiberoptic flexible sigmoidoscopy remain anecdotal and inconclusive. We prospectively evaluated three commonly recommended regimens for administering hypertonic phosphate enemas to subjects undergoing 60-cm fiberoptic flexible sigmoidoscopy for routine indications. Patients were randomly assigned to one of three hypertonic phosphate enema regimens. Group A received one enema 1 hour before fiberoptic flexible sigmoidoscopy, group B received two enemas 1 hour before, and group C received one enema 3 hours before and a second enema 1 hour before fiberoptic flexible sigmoidoscopy. Adequacy of bowel preparation was graded as excellent, adequate, or poor. Results revealed no statistically significant difference in the adequacy of bowel preparation between the three regimens, all resulting in adequate or excellent preparation in approximately 80% of patients. We recommend the use of one hypertonic phosphate enema 1 hour before routine fiberoptic flexible sigmoidoscopy. Implementation of this recommendation is efficacious, convenient for patients, and cost-effective.