This case-control study investigates the risk of cancers in adults aged 15-74 years, diagnosed between 1974-2003 in England and Wales, in relation to proximity of their home to overhead powerlines. The number of adults with residential exposure to significant electromagnetic fields from powerlines will also be estimated. Two hypotheses are being investigated. The first concerns the possible association between magnetic fields and risk of leukaemias, malignant melanomas, central nervous system and breast cancers. Residential exposure to the powerline is represented by modelled magnetic field strength and two distance-based measures. The second hypothesis involves the potential association between inhalation of charged particles downwind of powerlines and excess risk of respiratory system and mouth cancers. Exposure is assessed using a simple downwind/upwind measure, and modelled estimates that incorporate electric field source strength, wind speed, wind direction and distance. Magnetic field strength and charged particle exposure measures have been modelled by National Grid, who have also supplied data on the high voltage power line network. Controls comprise people diagnosed with non-exposure related cancers within the study period. Cases and controls were identified from the national cancer registry and residential addresses were geo-referenced within a GIS. Potential confounders include socio-economic status and urban-rural status and will be adjusted for in the analysis. The effects of migration will be explored using data from the UK Office for National Statistics (ONS) Longitudinal Study.