To identify demographic and clinical factors associated with pain improvement after a lumbosacral transforaminal epidural steroid injection (TFESI) for the treatment of radicular pain. Retrospective cohort study. Outpatient center. Adults (N=188) who underwent a fluoroscopically guided TFESI for lumbosacral radicular pain. Not applicable. Pain reduction from preinjection to 2-week follow-up was measured by visual analog scale (VAS). Patients were grouped by those who experienced no pain relief or worsened pain (≤0%), pain relief but <50% relief (>0%-<50%), or significant pain relief (≥50%) on the VAS. The mean duration of pain prior to injection was 45.8±81 weeks. The mean time to follow-up after TFESI was 20±14.2 days. Significantly more patients who experienced ≥50% pain relief at follow-up reported higher preinjection pain on the VAS (P=.0001) and McGill Pain Inventory Questionnaire (P=.0358), reported no worsening of their pain with walking (P=.0161), or had a positive femoral stretch test (P=.0477). No significant differences were found between VAS pain reduction and all other demographic and clinical factors, including a radiologic diagnosis of disk herniation versus stenosis or other neural tension signs on physical examination. Greater baseline pain on the VAS and McGill Pain Inventory, a history of a lack of worsening pain with walking, and a positive femoral stretch test predict a greater likelihood of pain reduction after TFESI for lumbosacral radicular pain at short-term follow-up. Greater baseline pain on the McGill Pain Inventory and a lack of worsening pain with walking predict a magnitude of >50% pain reduction.