A register study was performed in a Swedish county to investigate lung cancer mortality in a population exposed to air pollutants from ferro-alloy industries. During 1961–1975, 810 lung cancer deaths were analyzed. A strong relation between population density and lung cancer mortality was found. When this factor was controlled no differences in mortality rates were found between the communities with ferro-alloy industry and the remainder of the county. A general increase in lung cancer mortality most marked for males was found over this time period.