Located in the north-western part of Turkey, the province of Kastamonu has lately been receiving national attention because of its cultural and touristic attractions. This study assesses the environmental radioactivity levels of the region through measurements of indoor radon concentrations and indoor/outdoor gamma absorbed dose in air and radionuclide activities in surface soil and drinking water. The indoor Rn-222 activity concentration was found to be 98.4Bq/m(3) equivalent to an annual effective dose of 2.48 mSv. The indoor and outdoor gamma absorbed doses were measured as 54.81 and 48.03 nGy/h, respectively, corresponding to a total gamma radiation level (of terrestrial and cosmic origin) of 0.33 mSv/y. The activity concentrations in the soil samples collected from the study area were determined as 32.93, 27.17, 431.43 Bq/kg for the natural radionuclides U-238, Th-232 and K-40, respectively, and 8.02 Bq/kg for the fission product Cs-137. These natural radioactivity sources result in a terrestrial gamma level of 60 mu Sv/y. The water samples collected from the region carry an average of 0.0089 Bq/1 of gross alpha and 0.271 Bq/1 of gross beta activities which together cause an annual effective dose of 1.83 mu Sv. The measurement results obtained in this study indicate that the region has a background radiation level that is within the natural limits and shows no significant departure from the other parts of the country. (c) 2006 Elsevier Ltd. All rights reserved.