The role of the potential confounders, in particular other occupational and/or environmental exposures, should be considered. We observed a cluster of incidence and mortality for pleural cancer among men in the second exposure category; the absolute number of cases is low, but the relative risk is high. This cluster is due to occupational exposure to asbestos in the small industrial area in the second exposure category. There are other environmental factors in the study area due to the proximity of the highway and the urban area. We took into account the effect of exposure to vehicular traffic using predicted NO2 levels; the dispersion model for NO2 showed no overlap between the areas of high NO2 and the areas of high heavy metal levels. The traffic-related pollutants in this case would act, at least in theory, as negative confounders. However, when NO2 levels where considered in the analysis no important changes in the relative risk estimates were noted, even for respiratory mortality.