Transforaminal epidural steroid injections (TFESI) are widely used in patients with lumbar foraminal spinal stenosis. Previous studies have evaluated the effects of TFESI on lumbar foraminal spinal stenosis using only pain scores. However, no study has evaluated the effect of TFESI on pain scores and walking distance in patients with lumbar foraminal spinal stenosis. This study aimed to assess the effect of TFESI on pain scores and walking distance in patients with lumbar foraminal spinal stenosis stratified according to disease severity. This retrospective study reviewed the medical records of patients who received TFESI for lumbar foraminal spinal stenosis. A total of 128 patients were divided into the moderate and severe groups based on the extent of fat obliteration and the presence of nerve root compression. A significant decrease in the numeric rating scale (NRS) scores was observed in the moderate and severe groups compared with the corresponding baseline values 4 weeks after TFESI; however, the NRS pain scores were lower in the moderate group than those in the severe group. In addition, the proportion of patients who experienced pain reduction (≥50%) was higher in the moderate group than that in the severe group. The moderate and severe groups showed a significant increase in walking distance compared with the baseline values 4 weeks after the treatment. However, the walking distance values did not differ significantly between the moderate and severe groups. Furthermore, the degree of satisfaction was higher in the moderate group than that in the severe group. Lumbar TFESI may reduce pain scores and increase walking distance in patients with moderate or severe lumbar foraminal spinal stenosis. Patients with moderate foraminal stenosis had better pain relief outcomes than those with severe foraminal stenosis.