Indoor and soil gas Radon (Rn-222) concentration measurements were accomplished in two stages in Sivas, a central eastern city in Turkey. In the first stage, CR-39 passive nuclear track detectors supplied by the Turkish Atomic Energy Authority (TAEA) were placed in the selected houses throughout Sivas centrum in two seasons; summer and winter. Before the setup of detectors, a detailed questionnaire form was distributed to the inhabitants of selected houses to investigate construction parameters and properties of the houses, and living conditions of inhabitants. Detectors were collected back two months later and analysed at TAEA laboratories to obtain indoor Rn-222 gas concentration values. In the second stage, soil gas Rn-222 measurements were performed using an alphameter near the selected houses for the indoor measurements. Although Rn-222 concentrations in Sivas were quite low in relation with the allowable limits, they are higher than the average of Turkey. Indoor and soil gas Rn-222 concentration distribution maps were prepared seperately and these maps were applied onto the surface geological map. In this way, both surveys were correlated with the each other and they were interpreted in comparison with the answers of questionnaire and the geological setting of the Sivas centrum and the vicinity. (C) 2010 Elsevier Ltd. All rights reserved.