Abstract Study objectives To evaluate the quality of analgesia and the incidence of side effects of 2 different concentrations of levobupivacaine given as an equal milligram–bolus dose (5 mg) via patient-controlled epidural analgesia after abdominal surgery. Design Prospective, randomized, blinded study. Setting Postanesthesia care unit and surgical wards of a university hospital. Patients Forty-nine patients (41 with complete file) undergoing major lower abdominal surgery. Interventions The patients were randomly assigned to 2 groups: 1.5 mg/mL (bolus 3.3 mL, lockout 20 minutes, n = 26) and 5 mg/mL (bolus 1 mL, lockout 20 minutes, n = 23). The epidural catheter was inserted in the low thoracic level (T9-T12) before induction of a standardized general anesthesia technique. Measurements Demography, upper sensory block, visual analog scale scores at rest and after coughing, levobupivacaine and rescue morphine consumption, motor blockade, hemodynamics, postoperative nausea and vomiting, sedation, and patient satisfaction were recorded within the first 48 hours. Main results Both groups were similar with regard to demographics, upper level of sensory blockade (T8), and visual analog scale pain scores at rest and after coughing, as well as levobupivacaine and subcutaneous rescue morphine consumption. Motor blockade in the lower limbs was very low in both groups. Arterial blood pressure was slightly lower in the 5 mg/mL group during the first 24 hours ( P = 0.052). Five patients in the 1.5 mg/mL and 7 in the 5 mg/mL group had postoperative nausea and vomiting ( P = 0.43). No other side effects were recorded, and all of the patients were satisfied. Conclusions Administering the same dose of levobupivacaine in either a low or high concentration via patient-controlled epidural analgesia mode provides an equal quality of analgesia with no difference in the incidence of side effects.