[en] We describe the case of a 46-year-old woman suffering from an hyperalgic sciatica caused by a lumbar synovial cyst. These are uncommon lesions associated with degenerative spine disease. They may be asymptomatic or may produce symptoms resulting from nervous structures compression. They are commonly found at the L4-L5 level, the site of maximum mobility. Their etiopathogeny is still unclear but degenerative spinal instability is the strongest factor for their growth. MRI is the most effective for the diagnosis. Conservative management is usually unsuccessful. Resection with or without fusion remains the more appropriate therapeutic option.