Spontaneous infarction of the ligamentum flavum is a very rare cause of mielo-radicular compression. In the literature only four cases are reported, all characterized by a clinical history of slowly progressive mielo-radiculopathy and good outcome after surgical treatment. A 70 year-old female patient presented with a four months clinical history of spontaneous, sub-continuous, progressive lumbar pain with bilateral irradiation to the L4-L5 dermatomers, right leg monoparesis and hypoaesthesia affecting tactile, thermal and pain sensivity, urinary incontinence and constipation. CT scan and MRI evidenced an extradural ovalar lesion in correspondence of the L1-L2 levels, that exerted compression over the dural sac, dislocating it anteriorly. The patient underwent a L1-L2 laminectomy and the lesion was totally resected. Rapid improvement of the patient's symptomatology has been noticed in the postoperative period, with complete recovery during the following month. Histologic examinations demonstrated that the mass was a haematoma of the ligamentum flavum. It's our opinion, that a picture of ligamentum flavum haematoma should be taken into account in differential diagnosis of posterior mielo-radicular compression. The progressive growth of the haematoma may explain the long clinical history of these patients and surgical treatment, even if delayed, permits an excel-lent clinical outcome.