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In retrospective occupational studies, the degree of confounding by smoking depends on variation in smoking among job-related exposure groups. We assessed the relationship between job title and smoking behavior as part of a study on occupational exposures and lung cancer.A questionnaire on smoking was mailed to a sample of 11,986 trucking industry workers. Company records were used to gather other relevant information.The response rate was 40.5%. Among white males, the age-adjusted prevalence of ever smoking was highest among longhaul truck drivers (67%) and lowest among clerks (44%). Smoking rates among workers with other job titles were similar.Our results will be used to adjust for the differences in smoking among jobrelated exposure groups when assessing the association between particulate matter exposure and lung cancer mortality. Our study also suggests that an assessment of methods to control for smoking should be considered in the design of retrospective occupational health studies. Am. J. Ind. Med. 49:1013-1020, 2006. © 2006 Wiley-Liss, Inc.