Introduction: Osteoid osteoma is the third most common benign tumor of bone. The incidence of osteoid osteoma in the spine, particularly in the patients younger than five years, is low.
Case Presentation: Here, we report a case of osteoid osteoma located in the lumbar spine (L5) occurred in a 3.5-year-old boy. The patient was referred with a chief complaint of back pain for six months that was aggravated at nights. Furthermore, no apparent spinal deformity existed. Based on the clinical and imaging findings, the diagnosis of osteoid osteoma was made, and the surgical excision of the lesion was performed. The histologic examination of the extracted tissue confirmed the diagnosis of osteoid osteoma. 
Conclusions: The back pain alleviated the day after the operation, and he was event-free over 6-month follow-up visits. This report highlights the importance of osteoid osteoma in the differential diagnosis of spinal pain presented at any age.