The factor analysis of qualitative parameters carried out in 968 patients with lung cancer helped identify certain features which may play the key role in the development and, consequently, diagnosis of various types of the disease. In workers of major industries, smoking proved a significant factor of higher incidence of lung cancer. Formation of the habit at an earlier age, its intensity and concomitant occupational hazards were found to increase the risk of cancer, particularly, in males. Mass screenings and questionnaire--based interviewing of smokers are suggested. Young age and heavy smokers should be included in groups at risk irrespective of