The U.S. Environmental Protection Agency has updated its assessment of health risks from indoor radon, which has been determined to be the second leading cause of lung cancer after cigarette smoking. This risk assessment is based primarily on results from a recent study of radon health effects (BEIR VI) by the National Academy of Sciences. In BEIR VI, the National Academy of Sciences fit empirical risk models to data from 11 cohorts of miners, and estimated that each year about 20,000 lung cancer deaths in the U.S. are radon related. A summary, abstracted from the technical report, is given of the EPA’s risk assessment results and methods, including some modifications and extensions to the approach used in BEIR VI. Results include numerical estimates of lung cancer deaths per unit exposure, which had not been provided in BEIR VI.