Lignite contains various trace-metal natural radioactive contaminants. In the Eordea Basin, the most important lignite field in Greece, the authors conducted a proportional mortality ratio (PMR) study that compared the mortality rates of individuals who lived in the basin vs. a control group who resided in the city of Kilkis, over a 30-yr period. The following information was used in the study: (a) municipal registrations of deaths from neoplasms during the period from 1971 to 2000, and (b) detection of radioactive substances in samples obtained from excised lungs of individuals living in Eordea Basin who suffered from neoplasm. The corresponding registrations of deaths from neoplasm of the inhabitants of Kilkis, a city located outside the Eordea Basin, formed the control group. A diachronic increase of the PMR was detected as a result of neoplasms and, particularly, as a result of lung cancer in Eordea Basin. However, the above ratio did not exceed the corresponding PMR recorded in Kilkis. In 20 lung samples obtained from patients who had lived in Eordea Basin, and in 19 lung samples from patients in Kilkis, the activity of the radionuclides of uranium and thorium radioactive decay series, potassium-40, and cesium-137 was not higher than expected. No statistically significant difference was found between the inhabitants of the 2 regions, thus it was concluded that the increase in respiratory-system neoplasms was likely associated with the high prevalence of smoking among the regions' inhabitants. In future studies, a longer observation period and examination of more cases will be necessary to further investigate a possible association between radionuclides and lung neoplasms in the Eordea Basin.