Mortality and census data for 400 districts of England and Wales were analysed with respect to existing sites of nuclear power stations and sites where the construction of such installations had been considered or had occurred at a later date (potential sites). Excess mortality due to leukaemia and Hodgkin's disease in young people who lived near potential sites was similar to that in young people who lived near existing sites. Areas near existing and potential sites might share unrecognised risk factors other than environmental radiation pollution.