Multiple sclerosis (MS) is a leading cause of neurological disability in young adults. The most widely accepted hypothesis regarding its pathogenesis is that it is an immune-mediated disease. It has been hypothesised more recently that chronic venous congestion may be an important factor in the pathogenesis of MS. This concept has been named 'chronic cerebrospinal venous insufficiency' (CCSVI) and is characterised by stenoses of either the internal jugular or azygos veins, or both. It is suggested that these stenoses restrict the normal blood flow from the brain, causing the deposition of iron in the brain and the eventual triggering of an auto-immune response. The proposed treatment for CCSVI is percutaneous transluminal angioplasty, also known as the 'liberation procedure', which is claimed to improve the blood flow in the brain thereby alleviating some of the symptoms of MS.