As a result of the accident in the nuclear power plant at Chernobyl, USSR, a considerable increase in radioactive background radiation was noted in some regions of Sweden. In areas with high radioactive fallout an increase in the amount of lightning flashes was observed during the 1986 thunderstorm season. A statistical test shows that there is a risk of less than 1% that the observed difference has occurred by mere chance. ¿American Geophysical Union 1987