To determine the effectiveness of lumbar transforaminal injection of steroid for the treatment of radicular pain. Comprehensive systematic review. The primary outcome of interest was the proportion of individuals with reduction of pain by ≥50%. Additional outcomes of interest were a more-than-two-point reduction in pain score, patient satisfaction, functional improvement, decreased use of pain medication, and avoidance of spinal surgery. For patients with disc herniations, using the criterion of ≥50% reduction in pain, success rates across included studies (range) were 63% (58-68%) at one month, 74% (68-80%) at three months, 64% (59-69%) at six months, and 64% (57-71%) at one year. For patients with lumbar spinal stenosis, success rates across included studies (range) were 49% (43-55%) at one month, 48% (35-61%) at three months, 43% (33-53%) at six months, and 59% (45-73%) at one year, but there was a lack of corroboration from appropriately controlled studies. There is strong evidence that lumbar transforaminal injection of steroids is an effective treatment for radicular pain due to disc herniation. There is a lack of high-quality evidence demonstrating their effectiveness for the treatment of radicular pain due to spinal stenosis, though small studies suggest a possible benefit. Lumbar transforaminal injection of nonparticulate steroids is as effective as injections with particulate steroids.