The level of radon in domestic dwellings in Ankara, Turkey, was studied using CR-39 passive alpha track detectors. During the period 1996-1997 indoor radon concentrations were measured in approximately 200 houses during a 6 months' winter period. Detectors were placed in two separate rooms of which one was a living room and the other was the main bedroom. Subsequent measurements were performed at the Istanbul Çekmece Nuclear Research and Training Centre. Values obtained were between 2 and 408 Bq/m3. These long-term radon concentrations were found to follow a log-normal distribution. Median values for living rooms and bedrooms were 19 and 25 Bq/m3, respectively. Indoor radon concentration was found to be associated with presence of cracks on the walls, building material used for floor and walls and the type of ventilation and heating (p < 0.05).