Radon and its daughter decay products are thought to be the cause of 5% of lung cancer in the UK. This assessment has been made by the National Radiological Protection Board (NRPB) after a national survey of radon levels in homes, when more houses than anticipated were found to have high levels, and after a reappraisal upwards of the effectiveness of radon and its daughter products in causing lung cancer. A review of the scientific evidence reveals no direct evidence to incriminate radon or its decay products at the levels found in our homes in lung cell carcinogenesis. The issue involves different scientific disciplines and is highly complex. Debate between scientists is required and more epidemiological studies of lung cancer and low radon exposure are necessary. Meanwhile the indirect evidence linking low levels of radon exposure to lung cancer is insufficient to warrant the remedial action proposed by the NRPB and accepted by the UK government.