Tobacco and tobacco smoke contain minute amounts of some natural radionuclides such as 210Pb and 210Po, which are carcinogens. Intake of these radionuclides results in an increase of radiation doses to lung cells and tissues. Samples of the most frequently smoked cigarette brands were collected from the local market of Riyadh City, Saudi Arabia. Activity concentrations of 210Po were measured by alpha spectrometers, following the radiochemical separation of polonium. The average activity concentration (range) of 210Po was 15.1 (5.5–22.2) mBq/cigarette. Cigarette smokers who consume one pack (20 cigarettes) per day are inhaling an average of 151 mBq/day of 210Po and 210Pb each. The mean values of the annual effective dose for smokers (one pack per day) were estimated to be 237 and 309 µSv from 210Po and 210Pb, respectively.