Several thousand indoor radon measurements have been obtained for homes in northern Virginia. Compilations of these data according to the geologic units under the homes show that some units have relatively high or relatively low median indoor radon levels, and that these differences persist through all four seasons. An attempt to determine if soil radon and soil permeabilitycould yield similar results, in terms of relative indoor radon, was not successful. Care should be taken in using such measurements to characterize the potential for radon problems in established communities and in areas of as-yet undeveloped property.