The activity concentrations of U-238, Th-232, (40) K and Cs-137 radionuclides in 25 samples of tobacco leaves grown in Turkey have been measured using a high purity co-axial germanium detector. The measured activity concentrations for U-238 ranged from 3.6 to 22.5 Bq kg(-1) with an average of 9.8 Bq kg(-1), for Th-232 from 0.8 to 11.0 Bq kg(-1) with an average of 2.4 Bq kg(-1), and for (40) K from 360.3 to 1,479.5 Bq kg(-1) with an average of 810.0 Bq kg(-1). The concentrations of Cs-137, the residue of fallout from the Chernobyl reactor accident, were found to range from 0.2 to 2.1 Bq kg(-1) with an average of 0.5 Bq kg(-1). The results indicate that the average activity concentrations of U-238 and Th-232 lie within the range of measured values worldwide, whereas for (40) K the average was found to be higher. The average annual effective radiation doses from the inhalation of the corresponding tobacco smoke by an adult smoking 20 cigarettes per day was deduced to be 93.3 mu Sv y(-1) for U-238, 193.2 mu Sv y(-1) for Th-232, 5.6 mu Sv y(-1) for (40) K, and 292.1 mu Sv y(-1) in total. The average annual effective dose from Cs-137 was calculated to be 8.5 nSv y(-1). The resulting average annual effective radiation doses of 0.3 mSv due to the inhalation of natural radiation sources in tobacco were compared with studies worldwide and found much smaller than the worldwide average effective dose of 1.26 mSv. It is concluded that smoking may contribute a non-negligible fraction to the annual effective dose depending on cigarette consumption and activity concentration in tobacco. This study is the first in which natural and anthropogenic radioactivity in tobacco in Turkey was measured. Therefore, it is considered as a baseline study. Further studies are needed to investigate the role of tobacco refinement in the observed reduction of U-238 concentration of refined tobacco.