BACKGROUND: Although glucocorticoid therapy has been used in patients with lumbar radiculopathy for many years, the results of studies in literature are inconsistent. The aim of the study was to evaluate the effects of intramuscular betamethasone injection on pain, disability, quality of life and electroneuromyography (ENMG) findings in patients with lumbar radicular pain (LRP). METHODS: Patients with LRP (n = 98) were evaluated between July 2022 and June 2023. Sixty patients who met the inclusion criteria were randomized into two groups. Glucocorticoid group (GC) received intramuscular injection of betamethasone and Placebo group (PB) received isotonic sodium chloride. Visual analog scale (VAS), Oswestry disability index (ODI), Nottingham health profile (NHP) and ENMG were applied to both groups. Patients were evaluated before treatment and after first week, first month and third month of treatment. RESULTS: Significant improvements were seen in all clinical parameters in GC group. At the end of third month, VAS and NHP-Pain subscale scores improved significantly in both groups (p < 0.001) but the change of these values over time was statistically significant in favor of GC group (p = 0.03 and p = 0.044, respectively). The significant improvements observed in ODI, Energy and Physical Mobility subscales and Total scores of NHP in both groups (p < 0.05) revealed no significant difference between the groups over time. The ENMG data revealed no significant difference within the groups except the fibrillation potentials, which disappeared in both groups. CONCLUSION: Intramuscular glucocorticoid administration provided improvements on pain, disability and quality of life of patients with LRP. Especially the effects on pain scores were superior to placebo. No superiority over placebo on ENMG findings has been demonstrated and further studies are needed in this regard. CLINICAL TRIAL REGISTRATION: The study protocol was registered to Clinicaltrials.gov with the number NCT05571046 (retrospectively registered on 30/09/2022).