Radon exposure (mostly radon daughters) has been linked to lung cancer in numerous case-control studies performed in the US, Europe and China. There are approximately 21,000 deaths per year in the US due to radon-induced lung cancers. One of the most comprehensive radon studies performed in the US by Dr. R. William Field and colleagues found a 50% increased lung cancer risk even at the protracted exposures at the EPA's action level of 4 pCi/L. North American and European pooled analyses further support these findings. However, the discussion about the opposite results is still continuing, especially a 2008 retrospective case-control study of lung cancer risk which showed substantial cancer rate reduction for radon concentrations between 50 and 123 Bq/m3.