Introduction. Preparations with sodium phosphate have the best toleration, but studies show that the patients require at least 24 hours of diet. Patients and methods: A prospective study was designed, with 2 groups of patients prepared with sodium phosphate (Travad); one group with diet 24 hours and other with 12 hours. The objective was to evaluate the tolerance to the preparation. Results: 207 patients were included; 104 to group A (24 hours), and 103 to group B (12 hours). The age average of all the patients was 58.1 +/- 10.1 years. 139 (67.1%) were women. 72.2% of the patients in group A were hungry during the preparation process vs. only 8.7% of the patients in group B (p=<0.001). The quality of the preparation between the two groups did not show significant differences. Conclusion. The tolerance to the preparation for the colonoscopy with sodium phosphate is better when patients have a liquid diet only for 12 hours.