Rheumatic fever and rheumatic heart disease have a very high prevalence in Mexico. The analysis of 5531 cases registered in the National Cardiological Institute (Mexico), show that morbidity is related to climate, since the rheumatic index is much higher in zones where temperate-rainy climate predominates in comparison with tropical places. Mexican indians are as suceptible to rheumatism as whites, except in that their lower economical status makes them more suceptible to the disease. In Mexico, as well as in other countries rheumatism shows a clearcut tendency to diminish but still is the cause of cardiopathy in 1/3 of cardiovascular patients; improvement in economical conditions of the general population seems to be the cause of the decrease observed.