The knowledge of pretreatment factors playing a role in the evolution of a lung cancer is important for the choice of a therapeutic option in an individual patient but is also crucial when performing clinical research. The purpose of this paper is to review the prognostic parameters recognized in three distinct populations. For small cell lung cancer, disease extent and performance status are the most discriminant well known factors. Age, sex, lactic dehydrogenase serum level and mediastinal involvement provide complementary information. For non small cell lung cancer, operability status is the variable responsible for the greatest heterogeneity. TNM classification, histology, age and sex and probably knowledge of some biological values are useful data to improve accuracy in the prognosis of operable patients. For patients unresectable at diagnosis, disease extent and performance status are the most important prognostic factors to which age, sex and some biological parameters could be added.