BACKGROUND. Bowel preparation is a significant aspect of the flexible sigmoidoscopy procedure. Clear visibility of the bowel mucosa is critical for a thorough examination. The combination of a light breakfast in the morning and the application of 2 phosphate enemas a few hours before the examination is a safe and commonly used method of preparing a patient for a flexible sigmoidoscopy procedure. However, there is a paucity of objective data on the efficacy of this method of bower preparation. It has been practiced on the basis of intuition and clinical-experience. METHODS. In this prospective single-blinded randomized study 429 consecutive patients were assigned to receive 1 of 4 different bowel preparations before elective 60-cm flexible sigmoidoscopy. after completion of the procedure, the examiner gave a subjective rating of the quality of the preparation. The rating was determined on the basis of the percentage of bowel mucosa that was visible. RESULTS. Statistical analysis of results suggests no significant difference in frequency of favorable ratings between the 4 bowel preparations. CONCLUSIONS, This study substantiates the practice of having a light breakfast and 2 phosphate enemas as a method of bowel preparation for a flexible sigmoidoscopy procedure. Additional preparatory measures such as dietary restrictions and ingestion of phospho-soda oral saline laxative did not significantly enhance the quality of the examination.