The trial is a randomised trial comparing annual CT screening for lung cancer with no screening in 4104 smokers and former smokers between the age of 50 and 70 years. The goals are: 1) to evaluate if annual CT screening can reduce lung cancer mortality by more than 20 % (in collaboration with the NELSON trial in the Netherlands, 2) to evaluate psychological effects of screening including the effects of false positive diagnoses, and 3) to evaluate possible effects on smoking behaviour. The trial is funded in full by the Danish Ministry of Interior and Health.