Infectious arthritis of a lumbar facet joint is exceptional; only nine cases have been reported previously. We describe an additional case caused byStaphylococcus aureus.The standard radiographs of the lumbar spine were considered normal. The infection was ultimately detected with bone scintigraphy and precisely localized with computed tomography scan. Because of difficulties of imaging facet joints, infections at this site may be under diagnosed. This patient's severe lumbar pain responded fully to oral antibiotic therapy.