A 56-year-old man was hospitalized with a 2-day history of back pain and fever. A magnetic resonance (MR) scan taken on admission showed a facet joint effusion and soft-tissue abnormality posterior to the joint. Follow-up MR imaging confirmed the facet joint destruction and periarticular abscess. A biopsy specimen grew Staphylococcus aureus. MR imaging is helpful in detecting this rare infection in the earliest phase of the disease.