Although sauna bathing is a traditional means of treating rheumatism, its effects on rheumatic diseases have not been studied. Animal studies suggest that hyperthermia could have a favourable effect in cases of chronic rheumatic inflammation. More than fifty percent of patients find that sauna bathing alleviates rheumatic pain and improves joint mobility. The effect is similar in both inflammatory and non-inflammatory disorders. Nearly all men experience sauna bathing as helpful, whereas one-fourth of women find it detrimental. Rheumatic pain is exacerbated and joint mobility decreases on the day after a sauna. Exacerbation of pain is more obvious in non-inflammatory diseases, especially in fibromyalgia, than in inflammatory diseases, and more obvious in women than men. It can be prevented by proper cooling.