[en] The ²²²Rn concentration in air was measured in a thermal water spa used as a hydrotherapy centre in Tunisia. The associated health risk for employees and patients due to the inhalation of ²²²Rn and its progeny was estimated. A protection scheme for the employees of the spas has been designed. Results show that the ²²²Rn concentration varies in the range [33-589] Bq.m^-3. The ²²²Rn concentrations measured in the present study show lower values in comparison to those reported for the thermal spas of other countries. The ²²²Rn concentration in different rooms of the spa depends mainly on the ventilation rate. A model based on dosimetric approach was adopted to estimate radon risk considering the ²²²Rn concentration, the time spent in the spa, and the radioactive equilibrium factor F. The annual effective dose was found varying between 0.2 and 1.7 mSv for workers while the range for patients was from 2.8 10^-4 to 110 10^-4 mSv. These values are within the ICRP recommended value. (author)