We have made our study over a period of five months. Out of 553 patients admitted to the Thermal Clinic at Lavey-les-Bains, we observed 111 patients suffering from chronic low-back pain, noting the changes, both subjective and objective, during their three-week stay at the clinic. From the physical aspect, they were encouraged to increase lumbothoracic mobility. From the subjective aspect, an evaluation of pain and handicap level, was made using a visual comparison scale and the completion of a questionnaire. We concluded that, in the short term, thermal treatment resulted in an appreciable relief of pain for these patients. In the long term, however, in view of the changing developments in clinical measuring techniques it is not possible to estimate in advance the functional effectiveness of treatment.