OBJECTIVE Colonoscopy is associated with pain and discomfort in the majority of patients when performed without sedation. We performed a prospective and randomized study to compare warm water instillation and standard air-insufflation colonoscopy techniques without any sedation. METHODS The data of 122 patients (64 female and 58 male) were statistically analyzed. Patients were randomized into two groups by using computer generated list. In group A, standard colonoscopy with air insufflation was performed. In group B colonoscopy was performed by warm water infusion into the bowel. No analgesic, antispasmodic or sedative medications were used. After colonoscopy, the level of pain during colonoscopy experienced by the patient was measured using the visual analog scale (VAS). RESULTS There were no statistically significant differences in gender and average age between the two groups of patients. Cecal intubation was successful in all patients (100%). All colonoscopies were performed without complications. Patients who had colonoscopy with water immersion had a significantly lower level of pain on the VAS (4.09 vs 5.06), p = 0.041. CONCLUSIONS We confirmed the advantages of warm water instillation for colonoscope insertion in reducing pain without compromising the time to reach the cecum, success of cecum intubation or patient safety.