Seasonal indoor radon measurement studies have been carried out in four districts, namely, Jhelum, Chakwal, Rawalpindi and Attock of the Punjab Province. In this regard, CR-39 based detectors were installed in bedrooms, drawing rooms and kitchens of 40 randomly selected houses in each district. After exposing to radon in each season, CR-39 detectors were etched in 6M NaOH at 80°C and counted under an optical microscope. Indoor radon activity concentrations in the houses surveyed ranged from 15 ± 4 to 176 ± 7 Bq m^-3 with an overall average value of 55 ± 31 Bq m^-3. The observed annual average values are greater than the world average of 40 Bq m^-3. Maximum indoor radon concentration levels were observed in winter season whereas minimum levels were observed in summer season. None of the measured radon concentration value exceeded the action level of 200-400 Bq m^-3. The season/annual ratios for different type of dwellings varied from 0.87 ± 0.93 to 1.14 ± 1.10. The mean annual estimated effective dose received by the residents of the studied area was found to be 1.39 ± 0.78 mSv. The annual estimated effective dose is less than the recommended action level (3-10 mSv).

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