Indoor radon and soil radioactivity levels were determined for Erzincan province in Turkey. Indoor radon concentrations were determined in 89 dwellings using CR-39 passive Solid State Nuclear Track Detectors (SSNTDs) for four seasons. The mean annual Rn-222 activity concentration was found to be 119 Bq.m(-3). In the winter season, indoor radon concentrations showed the highest values while the lowest values were observed in the summer season. A model was used to predict the number of lung cancer incidences due to inhalation of radon. The findings have indicated that radon is responsible for 13% of lung cancer incidences occurring in the Erzincan province. Since indoor radon concentration correlates with Ra-226 content in soil beneath the dwellings, soil samples were collected near the houses where indoor radon measurements were performed in order to seek a correlation. The Ra-226, Th-232, K-40 and Cs-137 activity concentration values were 52, 26, 649 and 9 Bq.kg(-1), respectively. The annual effective dose due to naturally occurring radionuclides was around 82 mu Sv.y(-1) which is higher than the world average value of 70 mu Sv.y(-1). The results of the present study are expected to be a useful baseline data for future studies.