Septic arthritis of a lumbar facet joint is a rare clinical entity and most articles have reported a single case. There have been few studies that have evaluated the clinical and imaging features of septic arthritis of lumbar facet joints. The clinical data of 5 patients diagnosed with septic arthritis of lumbar facet joints were retrospectively studied. The average age of 5 patients was 73.6 years. All patients had elevated temperature at admission (37.7 degrees C). Leukocyte count was tested in all 5 patients and was elevated in only 2 patients. Erythrocyte sedimentation rate and C-reactive protein were examined and were elevated in all 5 cases. Magnetic resonance imaging was accurate in identifying the septic joint and associated abscess formation. All patients were treated with bed rest and received intravenous antibiotics for an average of 33.3 days. Four of 5 patients had positive outcomes with full recoveries and no evidence of recurrent infections. One patient exhibited evidence of recurrent infection and required open facet arthrotomy and paraspinal muscle debridement after intravenous administration of antibiotics. Septic arthritis of the lumbar facet joint is a rare cause of low back pain. It is important to ascertain the diagnosis at the earliest possible stage and to start intravenous antibiotics therapy as soon as possible. Magnetic resonance imaging is quite a sensitive modality for identifying infection of the lumbar facet joint. Familiarity with its clinical symptoms and radiographic features is necessary to avoid misdiagnosis of this condition.