The article constitutes an attempt to compare Polish and American coals in terms of their uranium and thorium content. As is known, uranium and thorium are radioactive elements that may constitute a danger to man during the process of exploiting and using coal for energy. That is why it is important to know where and what quantities of these elements can be found in coal. The article focuses mainly on bituminous varieties of coal originating from the Upper Silesian Coal Mining Area, although the results of studies conducted on coals from the Lower Silesian Coal Mining Area and Lublin Coal Mining Area have also been presented. For American coals, the results of studies conducted from the Western United States and Illinois Basin regions have been presented. In the Upper Silesian Coal Mining Area, the most highly mineralized uranium zones are marginal zones. Mineralization mainly concerns areas characterized by tectonic or sedimentary discontinuity, as well as areas where coal meets sandstone. The presence of uranium in coal is the effect of its leaching from upper layers, and subsequent infiltration into coal beds. Among the radioactive elements present in coals from the Upper Silesian Coal Mining Area, two different series of natural radionuclides can be found, above all: a uranium series with the mother isotope 238U, and a thorium series with the mother isotope 232Th. Isotopes of radium such as 226Ra (from the uranium family) and 228Ra (from the thorium family) can also be found within these series, among other things. The specific activity of these isotopes in coals from the Upper Silesian Coal Mining Area is respectively equivalent to 18 Bq/kg for the first isotope, and 11 Bq/kg for the second isotope. The maximum proportions of particular isotopes are much higher for coal dust as opposed to medium or large sized coal. This is most likely tied to the greater amount of ash in coal dust. The concentrations of radioactive isotopes observed in rocks that surround coal are many times higher than the values noted in the coal itself. Depending on the exploited coal bed and geological construction, coals from the Upper Silesian Coal Mining Area differ from each other in terms of the average specific activity of particular radioactive isotopes. The specific activity of natural radioactive isotopes is influenced by the amount of pollution and mineral composition. Commercial size of coal contain mineral pollution, in addition to pollution introduced during mining, which is not subsequently eliminated during the coal's processing and enrichment. In most of the samples of American coals the uranium content is equivalent to 1 - 4 ppm. Similar concentrations of uranium can be found in ordinary rocks and soils. The thorium content is also equivalent to 1 - 4 ppm. This value is low considering that the average thorium content in the earth's crust is equal to 10 ppm.