Background: Identifying risk factors for lung cancer in the population could improve the cost-effectiveness of early detection programs using thoracic computed tomography (CT). Aim: To examine the risk factors of lung cancer in a cohort of adult smokers. Patients and Methods: An annual clinical and respiratory functional assessment, chest computed tomography for three years and clinical follow up for five years was carried out in 270 patients aged 65±9 years, 55% males, active or former smokers of 10 or more pack-years . Results: Thirty seven percent of patients were active smokers, consuming 37±26 packs/year, 85% had comorbidities, especially chronic obstructive pulmonary disease (COPD) (66%), hypertension (48%), diabetes (22%) and dyslipidemia (42%). Thirteen percent of patients had family history of lung cancer. Twenty-one cases of lung cancer were detected in the five years follow up, especially squamous cell carcinoma and adenocarcinoma. In the univariate analysis, the main risk factors for lung cancer identified were an age older than 60 years, history of COPD, family history of lung cancer, active smoking, tobacco consumption more than 30 pack/year and lung hyperinflation. In multivariate analysis, the three independent risk factors for lung cancer were a family history of lung cancer, active smoking and the number of packs per year of tobacco consumption. Conclusions: The identification of risk groups probably will improve the performance of programs for early detection of lung cancer.Background: Identifying risk factors for lung cancer in the population could improve the cost-effectiveness of early detection programs using thoracic computed tomography (CT). Aim: To examine the risk factors of lung cancer in a cohort of adult smokers. Patients and Methods: An annual clinical and respiratory functional assessment, chest computed tomography for three years and clinical follow up for five years was carried out in 270 patients aged 65±9 years, 55% males, active or former smokers of 10 or more pack-years . Results: Thirty seven percent of patients were active smokers, consuming 37±26 packs/year, 85% had comorbidities, especially chronic obstructive pulmonary disease (COPD) (66%), hypertension (48%), diabetes (22%) and dyslipidemia (42%). Thirteen percent of patients had family history of lung cancer. Twenty-one cases of lung cancer were detected in the five years follow up, especially squamous cell carcinoma and adenocarcinoma. In the univariate analysis, the main risk factors for lung cancer identified were an age older than 60 years, history of COPD, family history of lung cancer, active smoking, tobacco consumption more than 30 pack/year and lung hyperinflation. In multivariate analysis, the three independent risk factors for lung cancer were a family history of lung cancer, active smoking and the number of packs per year of tobacco consumption. Conclusions: The identification of risk groups probably will improve the performance of programs for early detection of lung cancer.