The efficacy of gabapentin monotherapy was investigated against both acute or chronic radicular pain caused by lumbar disk hernia (LDH) or lumbar spinal stenosis (LSS). Seventy-eight patients with radicular pain, 10 males and 68 females aged 23 to 76 years (mean 49.4 years), caused by LSS in 45 patients or LDH in 33 patients were treated with oral administration of gabapentin and were followed up for 3 months. The evaluation included neurological examination, Odom's criteria, visual analog pain scale (VAS), and walking distance. Gabapentin treatment resulted in decreased VAS scores in both groups. Odom's criteria scores had improved to excellent or good in 36 patients with LSS and 28 patients with LDH. Furthermore, walking distance was significantly longer at the 3rd month of the treatment protocol. Eight patients discontinued gabapentin therapy because of the side effects. Gabapentin could be an option in the conservative management of acute or chronic radicular pain.