To estimate annual average concentrations in Korean dwellings and the effective dose to the general public, nationwide surveys on radon were conducted in 1989, 1999-2000 and 2002-2005. The total number of dwellings was about 5600. A survey of thoron and its decay products was also conducted in 2002-2005. In 2008-2009, a new radon survey in 1100 public buildings was conducted. The annual arithmetic (AM) and geometric (GM) means of indoor radon concentration in total were 62.1 ± 66.4 and 49.0 ± 1.9 Bq m(-3), respectively. The annual AM and GM means of indoor thoron concentrations were 40.4 ± 56.0 and 10.7 ± 2.9 Bq m(-3), respectively. The radon and thoron concentrations in detached houses were much higher than those in apartments. The locations of the high radon or thoron houses seem to be correlated with the concentrations of their parent nuclides in surface soil. The mean individual doses of radon and thoron were calculated to be 1.65 and 0.17 mSv y(-1), respectively.