As neurology and neurosurgery become more and more concerned with therapy there is a need to consider the results of the different treatment options in a strictly comparative mode. As new strategies for treatment of these disorders are devised the question has to be asked whether any new treatment supersedes, becomes part of the management of a condition, or is used only in certain circumstances. Since much treatment in neurology and neurosurgery has been developed empirically, evidence for efficacy is, in many instances, surprisingly sparse. Other treatments, for example, the treatment of cerebral aneurysms, or the use of aspirin in stroke prevention have been subjected to rigorous evaluation in multi-centre and, in some instances, in international clinical trials. In this book most conditions treated by neurologists or neurosurgeons are discussed in relation to the outcome of treatment. Only when the outcome of a given therapy is known can its value in relation to other treatments be considered, and full, informed advice be given to a patient. In a sense, this process is an extension of knowledge about prognosis. The reader will notice in this book the different approaches to the problem of outcome taken by the authors of the different chapters, and reflect that these relate to the differing levels of effectiveness of treatment, or of understanding of the disease under discussion. In some areas it is apparent that there is much data but, in others, the data are more descriptive than analytical. Clearly, there is a long way to go in the search for conquest of neurological disease.