Background: Owing to good solubility of radon 222Rn in water the gas is found almost in all surface and underground water basins. Radon released from water into the ambient atmosphere is a source of health hazard to the workers handling mineral water in Spa facilities. Material and Methods: Mean monthly radon concentrations were measured using closed dosimetry with CR-39 trace detectors. Of the 101 Spas included in the study, 76 returned the dosimeters. Results: In two Spas, the measured concentrations were above 1000 Bqm-3, and thus annual doses of over 6 mSv could be received by the workers of those Spas. In four of the Spas, radon concentrations were within the range of 500- 1000 Bqm-3. In the majority (75%) of the Spas, mean monthly radon concentrations were not higher than 150 Bqm-3. Conclusions: One hundred sixty persons working in 13 Spas can be exposed to the doses, which are important from radiation protection point of view. In the remaining Spas, radon exposure is maintained at the level of average exposure of the general population in Poland. Med Pr 2008;59(1):35-38