The lifetime lung cancer risk in inhabitants of the old city of Nablus has been estimated using the measured indoor radon concentrations in their homes. It is found that the lung cancer risk factor is higher in females as compared to males living in the same home. The lung cancer risk factor ranged between 33x10-4 to 54x10-4 and 47x10-4 to 77x10-4 for males and females, respectively.