Objective The intent of our study was to compare the effects of dexmedetomidine versus midazolam on perioperative hemodynamics, sedation, pain, satisfaction and recovery scores during colonoscopy. Material and methods A total of 60 ASA I-II patients, between 20 and 80 years of age were included in the study. Patients were randomly assigned to two groups. Midazolam 0.05 mg kg(-1) and fentanyl citrate 1 mu g kg(-1) were administered intravenously to cases in Group I (n=30). An initial loading dose of 1 mu g kg(-1) dexmedetomidine was administered intravenously in 10 min to cases in Group II (n=30) before the procedure and as a continuous infusion dose of 0.5 mu g kg(-1) h(-1) just before the procedure started. Also 1 mu g kg(-1) fentanyl citrate was administered intravenously immediately before the procedure. Peripheral oxygen saturation (Spo(2)), mean arterial pressure (MAP), heart rate (HR), Ramsay Sedation Scale (RSS), Numeric Rating Scale (NRS) scores and colonoscopist satisfaction scores of the cases were recorded. Results Although statistically significant values were not detected between the two groups with regard to mean arterial pressure, in Group I heart rates were higher and Spo(2) scores were lower in a statistically significant manner. When the groups were compared with regard to RSS, the RSS scores of Group I at the 10th and 15th minutes were significantly lower than Group II. There was no statistically significant difference between the two groups when compared with regard to NRS scores. Satisfaction scores were significantly lower in Group II. Conclusion Dexmedetomidine provides more efficient hemodynamic stability, higher Ramsay sedation scale scores, higher satisfaction scores and lower NRS scores in colonoscopies. According to our results we believe that dexmedetomidine can be used safely as a sedoanalgesic agent in colonoscopies. Eur J Anaesthesiol 2010;27:648-652