The aim of this study was to investigate a possible relationship between occupational exposure to vehicle exhaust and cancer risk. For this purpose, a cohort of 14,225 truck drivers was followed throughout a ten-year period with regard to cause-specific mortality. Comparisons were made with another cohort of unskilled male laborers. Both of the occupational groups compared were identified at a census and no supplementary data on individual exposure history were available. The study showed an increased mortality for lung cancer (standardized mortality ratio (SMR) 160, 95% confidence interval (CI) 126-200) and multiple myeloma (SMR 439, 95% CI 142-1,024). It seems likely that exposure to diesel exhaust has contributed to the increased lung cancer risk observed. The possible relationship between multiple myeloma and certain constituents of vehicle exhaust may be worth attention in future investigations.