The purpose of this document is to provide recommendations for the selection of the optimal target population for lung cancer screening trials with Spiral Computer Tomography based on an analysis of risk factors and high-risk populations. Our recommendations are to include current or ex-smokers (<5 years) with a smoking history of at least 30 years and an average consumption of at least 20 cigarettes a day. When these selection criteria are applied there is no need for a lower age cut-off. Elderly people can be included as long as their life expectancy is more than 10 years. Participants should be fit enough to undergo thoracic surgery. They may have a history of previous cancer, provided that the cancer has been curatively treated at least 5 years ago without evidence of relapse, except for breast cancer, melanoma and hypernephroma. People with an inability to lie flat, who are unable to hold their breath for 20 s, with a body weight above 140 kg, a chest CT scan within 1 year before enrolment or a previous pneumonectomy should not be invited. The inadequacy of the unit 'Pack-Years' (PY) to estimate the individual lung cancer risk is recognised, and future initiatives to develop an appropriate lung cancer risk model are encouraged.