The province of Ferrara represents one of the areas with the highest mortality rate for lung cancer in Italy. The aim of the study is to evaluate the relative importance of the main known risk factors for lung cancer in that area. It is a case control study based on the population where the cases under study (249) are selected from subjects deceased over the period 1988-1993 in the territory of the ex USL 33 (Local Health Authority) of Comacchio, while the controls (500) lived in the same area. The statistical analysis showed the same information that can be found in other medical literature regarding the known risk factors: smoking (OR = 3.7-44.9 per n. cigarettes/die), spouse passive smoking (OR = 1.1), passive smoking due to social setting (pubs) (OR = 1.9), vegetable diet (OR = 0.4). A important role was played by the factors linked to socio-economic differences. There was a significant increase in risk for those who had lived in "casazze" in the area, which are typical homes of the poorer social classes. There was also a significant increase in risk for subjects with a lower level of education. To obtain these results the analysis method known as "classification trees" was also used in order to verify its possible use in the public health sector.