Background Data: Ligamentum flavum cysts have rarely been reported, it is believed to be a result of degenerative process. Complete excision of the cyst leads to excellent results. Ligamentum flavum cysts have rarely been reported worldwide and never published as an Egyptian case. Purpose: To report a case of ligamentum flavum cysts in the lumbar spine. Study Design: Case Report. Patients and Methods: We reported a case of ligamentum flavum cyst at the level of L4-5 in a 45 year old Egyptian woman, meticulous complete excision of the cyst without any durotomy or CSF leakage. Histopathological examination reported myxoid degeneration of the ligamentum flavum with no synovial cells. Results: the patient was satisfied and all her symptoms were completely resolved with 1 year follow up. Conclusion: ligamentum flavum cyst should be put in mind when reading the MRI. Complete surgical excision should be carried meticulously. (2016ESJ123)