The main objective of this study is to assess the health hazards due to radon gas accumulation and to compare the concentrations in different kinds of workplaces, in the city of Adapazari, one of the most important industrial cities of Turkey. For this purpose, radon activity concentration measurements were carried out in schools, factories, offices and outdoors using CR-39 solid state nuclear track detectors (SSNTD). Results show that the mean radon activity concentrations (RAC) in schools, offices and factories were found to be 66, 76 and 27 Bq/m(3), respectively, with an outdoor concentration of 14 Bq/m(3). The average concentrations were found to decrease as follows for different types of industries: automotive > electronic > metal > textile. Because the maximum measured radon concentrations are 151 Bq/m(3) in the schools, 173 Bq/m3 in the offices and 52 Bq/m(3) in the factories, the limits of ICRP are not exceeded in any of the buildings in the region. In addition, the estimated mean annual effective doses to the people in the workplace, students, office workers and factory workers have been calculated as 0.27, 0.63 and 0.20 mSv/y, respectively for the region.