An 86-year-old man presented with intermittent claudication caused by a cyst of the ligamentum flavum. Lumbar magnetic resonance imaging demonstrated an extradural cystic mass at the L5-S1 intervertebral space and canal stenosis at the L4-5 space. L-5 laminectomy and flavectomy at the L4-5 and L5-S1 spaces were performed, and the cystic mass was excised. The histological features were consistent with cyst of the ligamentum flavum. The histological diagnosis was ganglion cyst of the ligamentum flavum. After surgery, claudication completely disappeared and the patient made a good recovery.