A 19-year-old boy presented with a 3-month duration of intermittent low back pain. SPECT imaging and CT scan confirmed the diagnosis of osteoid osteoma in the left pars inter-articularis of the L4 vertebra. Surgical enucleation of the tumour, curettage and bone grafting was performed through a posterior approach. The pars inter-articularis of L4 is an unusual location of the tumour. Early surgery resulted in a successful outcome.