Cysts of the ligamentum flavum of the lumbar spine have seldom been described. They are clearly visible in computed tomography as well as nuclear magnetic resonance, but are frequently wrongly diagnosed as ganglion or synovial cysts. The correct diagnosis is not feasible until after surgery. Such space occupying lesions can most often lead to uniradicular pain due to compression of a root. These cysts should be viewed as part of the degenerative process of the spine but not as tumor lesions. They need to be removed only in case of root entrapment. On the basis of six of our cases treated by surgery we describe the symptoms, imaging findings, operative techniques and pathological investigations.