BACKGROUND Dexamethasone is an available and cheap drug and has low complications. There are not enough studies on antiemetic and analgesic effects of dexamethasone after laparoscopic cholecystectomy. The aim of this study was to assess the efficacy of single-dose of dexamethasone on Postoperative Pain (POP) and Nausea and Vomiting (PONV) in the patients undergoing laparoscopic cholecystectomy in northern Iran. MATERIALS AND METHODS This randomised controlled trial was conducted on 140 patients who were candidates for laparoscopic cholecystectomy. The subjects were randomly assigned into Group I (dexamethasone 8 mg) and Group II (normal saline 5 mL). Each group had 70 patients. The subjects were followed about POP and PONV every 4 hours for 12 hours after the operation using Nausea and Vomiting Scale (NVS) and Visual Analogue Scale (VAS) pain scores. RESULTS Seven patients (12.1%) were men and 123 (87.9%) were women. The mean age was 44.37 ± 8.69 years old. The mean NVS score was significantly different between the two groups in both periods 0-4 hours (Group I: 1.06 ± 0.85, Group II: 1.38 ± 1.00; p= 0.043) and 4-8 (Group I: 0.58 ± 0.24, Group II: 0.67 ± 0.29; p= 0.047) hours after the surgery. About VAS pain score, there were significant mean differences between the two groups in both periods 4-8 hours (Group I: 4.09 ± 1.01, Group II: 4.49 ± 1.24; p= 0.038) and 8-12 hours (Group I: 2.06 ± 0.81, Group II: 2.47 ± 1.16; p= 0.017) after the surgery. CONCLUSION According to the findings, single-dose of dexamethasone had a significant reducing effect on POP and PONV in the patients undergoing laparoscopic cholecystectomy.