Septic arthritis of the posterior lumbar joints is extremely rare in comparison with spondylodiscitis which is much more common. We report a case of an 86-year-old women with septic arthritis of the left L4-L5 lumbar facet joint associated with endocarditis. Arthritis diagnosis was made on CT scan and MRI, infection by Staphyloccocus aureus was proved by blood cultures. Heart growth was seen by echocardiography. Twenty-three cases were reported in the literature. Clinical and biological data failed to discriminate between facet joint septic arthritis and spondylodicitis. Diagnosis is established on imaging findings, computed tomography and magnetic resonance imaging, completed by blood cultures and, if they are negative, by aspiration-biopsy. Appropriate antimicrobial therapy is usually successful. Some back pain generally persists. In conclusion, lumbar pain with fever without spondylodiscitis is suggestive of septic arthritis of a lumbar facet joint. Epiduritis associated in 60% patients requires rapid treatment.