There are large number of spas in Spain and there is a lack of data concerning their radioactivity. The levels of radioactivity in a wide sample of Spanish spas were measured with special attention being paid to the radon and radium concentrations in the water, and to radon concentration in the indoor air of the spas. This study is primarily concerned with the radioactivity of the spas of one region in Spain--Cantabria--and particularly one spa where we measured radon levels in water as high as 824 Bq/l and over 5000 Bq/m3 in the air of the rooms. We then considered a wider sample including virtually all of the radioactive spas in the country. The results indicate that a fairly large number of spas have radon levels in water that are moderately high and they are used for the treatment of diseases without radiation protection measures for patients or staff at the spas.