The major contribution to population exposure from natural radiation arises from the inhalation of the decay products of radon. Substantial surveys are being conducted by several investigators to estimate the indoor and outdoor exposure nationally and to discover regional variations. In this work, radon concentration in the indoor and outdoor air was determined using the can technique and employing CR-39 solid state nuclear track detector for lengthy exposures. The range of radon-222 activity in this survey was 54 … 299 pCi · m−3in Cairo, 22 … 171 pCi · m−3in Alexandria and 89 … 370 pCi · m−3in Asiut. Measurements carried out in Aswan and Sinai ranged between 98 … 411 pCi · m−3. Values of indoors and outdoors radon concentrations were found to vary with geographic location, season and height above ground. Further work is going on to study the different parameters affecting the levels of the environmental radon.