Background: Osteoblastomas (OTB) with co-existent aneurysmal bone cysts (ABC) of the spine are extremely rare and more so in the lumbar spine. To the authors’ knowledge, only one case of lumbar spine involvement has been reported in a paediatric patient. Objectives: To highlight diagnostic challenges and surgical management of co-existent lumbar OTB-ACB in a child. Methods: We present a 14-year old female with low back pain and progressive swelling of 2 months. She was evaluated by neuroimaging studies and histopathological assessment of resected tissue. Results: X-ray showed a lytic lesion in L3 with loss of the left pedicle. Magnetic resonance imaging (MRI) revealed a fluid-filled, heterogeneously enhanced, lobulated lesion posterior to the vertebral bodies of L3, L4 and L5, which infiltrated the quadratus lumborum muscles bilaterally, and histologically diagnosed as ABC. The L3 pedicle also revealed an expanded, heterogeneously enhanced mass lesion which appeared to be different and showed no fluid-filled levels, histologically diagnosed as OTB. Surgical intervention involved tumour excision with partial spondylectomy of L3 vertebra, posterior instrumented stabilization and fusion. Conclusion: The case highlights the diagnostic challenges of co-existent OTB-ABC and the significant role of surgical management via spinal reconstruction, stabilization and fusion after gross total tumour excision.