Background/aims: Oral sodium phosphate is an agent used commonly in our country for cleaning the intestines before colonoscopy. Our aim was to compare the safety, tolerability and efficiency of oral sodium phosphate solution used in colonoscopy preparation in patients over 70 years of age. Methods: This study was carried out in Ankara University School of Medicine Cebeci Hospital Endoscopy Center between August 2008 and March 2009. The extent of colon cleanliness was scored in the colonoscopy procedure. The data from the two groups were compared. Results: In our study, 55 patients were divided into two groups according to their age, as over 70 years (n: 25) and under 70 years (n: 30). The average age of the group under 70 years was 49.4 +/- 9.8 and of the group over 70 years was 71.4 +/- 1.2 (p=0.04). Among the patients included in this study, 59.1% were female (n: 28) and 50.9% were male (n: 27). In the over 70 years group, the intestinal cleanliness was poor-fair in 2 patients, acceptable in 7 patients and excellent in 16 patients. In the below 70 years group, the intestinal cleanliness was poor in 2 patients, acceptable in 9 patients, good in 13 patients, and excellent in 6 patients. In the statistical evaluation, it was determined that there was no statistical difference between the over- and below 70 years of age groups regarding good-excellent intestinal cleanliness and poor-medium intestinal cleanliness (p=0.109). There was no statistical difference between the groups with regard to the adverse effects. The sodium, potassium and creatinine levels were assessed on the procedure day in 5 patients with clinical side effects (abdominal pain, nausea, vomiting, dizziness, hypotension) in the elderly group. No electrolyte imbalance or renal function impairment was observed in these patients. Conclusions: In the group of patients over 70 years old, a special patient group without comorbid diseases, oral sodium phosphate solution used for colon preparation was effective and well- tolerated with a low adverse effect rate. In spite of this safe profile, since serum creatinine levels and electrolyte imbalance were assessed in only a limited number of patients, the relationship reported in the literature between oral sodium phosphate and electrolyte imbalance and renal function impairment should be kept in mind.