A recent retrospective mortality study, based on proportionate mortality ratios (PMRs), has shown that blue-collar automotive workers have an excess of approximately 30% in lung cancer deaths over a comparable representation of the general population. This study compares the cigarette smoking habits of automotive workers with those of the general population and assesses the extent to which any smoking habit differences might account for the excess in lung cancer deaths among automotive workers. The results show that when smoking differences are considered, the lung cancer PMR for white male automotive workers declines from 103 to approximately 1.1. These findings suggest that smoking habits of a studied population can affect mortality ratios for lung cancer when the smoking habits of the studied population differ significantly from those of the general population.