Compared with spinal epidural hematomas, spinal subdural hematomas are rare; chronic forms are even more uncommon. These hematomas are associated not only with lumbar puncture and spinal trauma, but also with coagulopathies, vascular malformations and tumors. Compression of the spinal cord and the cauda equina means that the patients develop increasing back or radicular pain, followed by paraparesis and bladder and bowel paralysis, so that in most cases surgical decompression is carried out. On magnetic resonance imaging these hematomas present as thoracic or lumbar subdural masses, their signal intensity varying with the age of the hematoma. We report the clinical course and the findings revealed by imaging that led to the diagnosis in three cases of chronic spinal subdural hematoma.