In 1986 the accident at the nuclear reactor in Chernobyl in the former Soviet Union released large amounts of radioactivity into the atmosphere. Adjacent areas were heavily contaminated, while more distant regions were affected less. International committees concluded that valuable information on the effects of radiation might result from long term follow up of workers affected by the accident, many of whom received doses in the range of 250-1000 mSv. The committees also recommended that studies should be carried out of residents living within a 30 km radius of the reactor and of residents of substantially contaminated regions in Belarus, the Ukraine, and Russia, who may have received doses of 50-60 mSv. The scientific value of investigations in Europe and other parts of the former Soviet Union was questioned, however, because estimated exposures (<1 mSv) were believed to have been too low to cause a detectable excess of cases of cancer or genetic defects.1 For comparison, annual doses from natural background radiation are 1-2 mSv.2

Nevertheless, because of widespread concern among populations in Europe living in areas of low fallout, the International Agency for Research on Cancer organised the …