The purpose of the research reported in this article was to reconstruct a typology of the various courses taken by rheumatoid pelvis-spondylitis based on medical evidence and then to assess the economic and social consequences of the illness generally and for each of the groups brought out by our research. The investigation dealt with 172 patients who had either been hospitalized or had consulted outside physicians or community clinics in the Nord-Pas-de-Calais Region or Paris. Between January 1978 and May 1979, these patients were asked to report to the places where they had had their consultations. Using the information in their medical records, the patients' statements and additional examinations, the case histories were pieced together, the patients' current condition was described and the typology of the disease was constructed. Then we collected the economic data and the disease's costs were reconstructed (medical costs, cost of losses in output, costs under the heading of either the individual or the community). Finally, data of a psychosocial nature made it possible to clarify the patients' understanding of the disease according to various criteria (particularly the different forms taken by the disease). The analysis of clinical, radiological, biological investigations makes it possible to bring out three trajectories of the disease. We have brought to light medical and economic costs of the disease clearly differentiated according to the trajectories of the illness. We have also underlined the role played by social factors in determining how the disease is perceived. Finally, the analysis of the effectiveness of known therapies shows that these therapies aim above all at easing the pain and limiting the stiffness and that a delay in applying these therapies does not seem decisive for the seriousness and the progression of the illness.