The side effects of the different hydrosoluble iodine contrast media now in use in neuroradiology are analyzed: ionic monomers, ionic monoacid dimers, nonionics. Their neurotoxicity depends on the patient, the product and its chemical structure, and the modes of administration. The available products, neurotoxicity after intravascular injection, and neurotoxicity after intrathecal injection are successively considered. The frequency of different complications and their pathophysiology are detailed for both injection modes. The authors propose a practical approach, choosing in each case the product with the best cost-efficacy coefficient. This choice must take into account the patient, the indications, and the product.