We report a 67-year-old man who presented with a 3-month history of progressively increasing pain in the lumbar spine. His past medical history was unremarkable, and physical examination disclosed local tenderness over the lower spine. No neurologic dysfunction was identified. Routine laboratory evaluation including alkaline phosphatase activity was normal. An X-ray film of the lumbar spine showed enlargement and increased density of L-5 vertebra. A whole-body bone scan revealed markedly increased uptake at the L-5 level. To further evaluate the nature of the disorder and the cause of his pain, a computed tomography (CT) scan was obtained. It disclosed multiple lucent areas with some sclerotic changes mainly affecting the vertebral body of L-5. No spinal stenosis was found. Subsequently, a bone biopsy of L-5 was performed that showed typical findings consistent with Paget's disease. The patient was treated with etidronate (200 mg b.i.d. for 6 months) followed by salmon calcitonin (50 IU 3 times/week s.c. for 6 months). The pain declined gradually in severity and the patient became symptom free after 12 months of treatment. A repeat X-ray film, obtained at that time, showed no significant change. However, a bone scan showed almost complete normalization. The present case illustrates that a high index of suspicion is required when only a single vertebra is affected by Paget's disease, especially, when alkaline phosphatase activity is normal. It may present with severe pain without evidence of neurologic dysfunction. CT scan may be a useful adjunct in establishing the diagnosis and elucidating the cause of pain.