BACKGROUND: Propofol is an accepted method of sedation for an ERCP and generally achieves deep sedation rather than conscious sedation, and dexmedetomidine has sedative properties of equivalent efficacy. OBJECTIVE: To examine the hypothesis that dexmedetomidine is as effective as propofol combined with fentanyl for providing conscious sedation during an ERCP. DESIGN AND SETTING: Randomized, blind, double-dummy clinical trial. PATIENTS: Twenty-six adults, American Society of Anesthesiologists status I to III, underwent an ERCP. INTERVENTIONS: Patients were randomized to receive either propofol (n = 14) (target plasma concentration range 2-4 microg/mL) combined with fentanyl 1 microg/kg, or dexmedetomidine (n = 12) 1 microg/kg for 10 minutes, followed by 0.2 to 0.5 microg/kg/min. Additional sedatives were used if adequate sedation was not achieved at the maximum dose allowed. MAIN OUTCOMES MEASUREMENTS: The sedation level was assessed by the Richmond alertness-sedation scale and the demand for additional sedatives. Furthermore, heart rate, blood pressure, oxygen saturation, and respiratory rate were continuously assessed. RESULTS: The relative risk (RR) was 2.71 (95% CI, 1.31-5.61) and the number of patients that needed to be treated (NNT) was 1.85 (95% CI, 1.19-4.21) to observe one additional patient with drowsiness 15 minutes after sedation in the dexmedetomidine group. Also, the RR was 9.42 (95% CI, 1.41-62.80), and the NNT was 1.42 (95% CI, 1.0-2.29) to require additional analgesic. However, there was also a greater reduction in blood pressure, a lower heart rate, and greater sedation after the procedure. CONCLUSIONS: Dexmedetomidine alone was not as effective as propofol combined with fentanyl for providing conscious sedation during an ERCP. Furthermore, dexmedetomidine was associated with greater hemodynamic instability and a prolonged recovery.