The value of prospective long-term studies on the features and course of multiple sclerosis is determined by the reliability with which relevant infor­ mation is documented. This involves two basic problems: I) The docu­ mentation system used must be detailed enough to provide adequate data on the essential features and course of the disease in a given case; on the other hand, it must not be so complicated and cumbersome as to preclude its use in the routine care of MS patients. 2) Since no system can fully anticipate new problems and scientific approaches that may become impor­ tant at some future time, the system must be open to provide the possi­ bility of adding and correlating the data of special research studies with the . basic data. These considerations led to the development of the basic documentation system described here and employed for the analysis of clinical data in this monograph. The work was carried out with the help of the Deutsche Forschungsgemeinscha/t as a part of its research program on multiple sclerosis and related demyelinating disease. A basic documentation pool including the data of more than 2 000 patients has been accumulated in the last six years. The system has been put to practical use in a number of epidemiologic surveys completed or under way, in following up the cases in an epidemiologic observation area in South Lower Saxony, and in studies on spasticity, cerebrospinal fluid findings, clinical forms and neuro­ physiological aspects of MS.