Osteoid osteoma is a benign bone tumor that rarely involves the spine. In this paper, an osteoid osteoma of the L5 vertebra, involving the left pedicle, has been presented. A 21-year-old male patient presented with low back pain, which worsens at night. Neurological examination was normal. Computed tomography of the lumbar spine has revealed a lesion with an oval nidus surrounded by sclerosis, involving the left pedicle of the L5 vertebra, which was considered as an osteoid osteoma. The patient was operated on and the tumor was completely removed. Histopathological examination was confirmative. The patient was discharged 2 days after the surgery as pain-free. Osteoid osteoma, although rarely involving the spine, should be included in the differential diagnosis of patients presenting with low back pain, especially if the patient is young and the pain worsens at night. ©2008, Firat University, Medical Faculty.