Study Objective: The aim of this study was to evaluate whether sedo-analgesia with alfentanyl/fentanyl, using a patient-controlled analgesia (PCA) pump, may have positive outcomes in terms of safety, postprocedural workload, and expectations of the colonoscopist, nurse, and patients in elective colonoscopy. Patients: One hundred American Society of Anesthesiology physical status I and II adult patients. Interventions: Patients were randomized in a double-blind trial to receive either alfentanyl (n = 50) or fentanyl (n = 50) by PCA, and incremental doses of midazolam. Measurements: Patient expectations were assessed using hemodynamic variables, willingness to have a repeat colonoscopy in the same way, adverse events, discomfort scores, and patient/operator/nurse satisfaction associated with sedo-analgesia. Result: All patients in both groups had adequate sedo-analgesia with high satisfaction and willingness scores. There were no serious adverse effects and except for a few events, no required medication. The total sedation times were shorter in the alfentanyl group compared with the fentanyl group. Conclusions: PCA and sedation with alfentanyl and fentanyl for colonoscopy are safe, feasible, and acceptable to most patients. However, shorter sedation times make alfentanyl more attractive for postprocedural workload.