To compare parasagittal interlaminar cervical epidural steroid injection (PSIL-CESI) and the classic midline interlaminar cervical epidural steroid injection (MIL-CESI) in terms of pain relief and functional improvement in patients with unilateral upper extremity radicular pain. This was a randomized clinical trial being conducted in a single pain center in Tehran. Twenty-six patients were allocated into two groups of 13, undergoing either PSIL-CESI or MIL-CESI. After confirmation of radiocontrast spread in the epidural space by fluoroscopic guidance, dexamethasone 8 mg and bupivacaine 0.125% in a volume of 5 ml were delivered to the epidural space. Evaluation of functional state and pain intensity before and 1 month after the procedure was accomplished using the neck disability index (NDI) and the numeric rating scale (NRS) respectively. Demographic and baseline characteristics of the cases showed no significant statistical difference. Improvements in the NDI and the NRS were observed in both groups; meanwhile, improvements were more pronounced in the PSIL-CESI group as compared to the MIL-CESI group (P<0.001). With the PSIL approach the ventral spread of radiocontrast was significantly higher (38%) than with the MIL approach (0.7%) (P<0.001). All patients in PSIL group showed radiocontrast spread ipsilateral to the painful side and all patients in the MIL group showed a midline distribution of radiocontrast. PSIL-CESI provides superior pain relief and improvement of functional disability in patients with unilateral upper extremity radicular pain in comparison to the classic MIL-CESI. IRCT20180524039816N1.