Exposure to ionizing radiation increases the risk of cancer in humans. Nuclear workers receive low doses over a relatively long period of time. METHODS: A mortality study of a cohort of workers exposed to ionizing radiation at Electricite de France (EDF) was conducted. The cohort consisted of 22,395 individuals monitored for radiation exposure between 1961 and 1994, and followed-up for an average of 11.7 years. RESULTS: Our study demonstrates a clear healthy worker effect (HWE) since mortality is less than half what is expected from National mortality statistics. The HWE is greater among workers who have spent most of their career in the nuclear sector. The analysis by cancer site shows no excess compared with the general population. No significant trend was observed according to level of exposure to ionizing radiation. CONCLUSIONS: The mortality of workers exposed to ionizing radiation at the French National Electricity company is very low compared to the French national mortality. (R.A.)