A patient with Marfan's syndrome had spontaneous intracranial hypotension secondary to a proved CSF leak. It is postulated that the leak was caused by minor, unrecognised trauma rupturing spinal arachnoid diverticula. The diverticula were probably pre-existing abnormalities complicating the Marfan's syndrome. It is concluded that patients with spinal meningeal defects may be at increased risk of developing CSF leaks, possibly secondary to unrecognised trauma.