Background: Interscalene brachial plexus block (IBPB) has gained importance for surgical purposes and pain management. It provides effective postoperative pain relief essential for patient comfort andearly ambulation. Objective: To evaluate the effect of dexamethasone as adjuvant to levobupivacaine in ultrasound-guided IBPB in shoulder and upper arm surgeries, and which route, the perineural or the intravenous was more effective. Patients and methods: Ninety patients randomly allocated into 3 equal groups: Group L: received IBPB with 20 ml of 0.5% levobupivacaine plus 2 ml normal saline (NS) with intravenous (iv) 10 ml NS. Group LD_P: received IBPB with 20 ml of 0.5% levobupivacaine plus dexamethasone 4 mg diluted in 2 ml NS with iv 10 ml NS. Group LD_IV: received IBPB with 20 ml of 0.5% levobupivacaine plus 2 ml NS with iv dexamethasone 4 mg diluted in 10 ml NS. Results: Patients in group LD_P took prolonged time to ask for the first request for analgesia compared with patients in group L and group LD_IV (15.57±3.89 vs 13.23±2.65 and 13.57±3.22, respectively) (p=0.007 and p=0.02, respectively), but no significant difference between group L and group LD_IV (p=0.696). Pethidine consumption was significantly increased in patients of group L compared with patients in group LD_P and group LD_IV (p < 0.001 and p < 0.001, respectively), but no significant difference in pethidine dose between group LD_P and group LD_IV (p=0.283). Conclusion: This study concluded that the addition of dexamethasone as an adjuvant to perineural levobupivacaine for IBPB prolonged the duration of analgesia, decreased the postoperative pain score, decreased pethidine consumption and improved patient satisfaction.