OBJECTIVE: To investigate the risk of cancer among workers exposed to diesel emissions in a large record-linkage study from Sweden. METHODS: The Swedish Cancer Environment Register III contains nationwide data on cancer incidence during 1971-1989, by occupation and industry of employment as reported in the 1960 and 1970 censuses. After excluding farmers, we classified job and industry titles according to estimated probability and intensity of exposure to diesel emissions. Exposed men in the 1960 census contributed over 7,400,000 person-years, and exposed women contributed over 240,000. We compared them to the remainder of the employed population, using indirect standardization and multivariate Poisson regression analysis. RESULTS: Men exposed in the 1960 census experienced an increased risk of lung cancer: the relative risks (RRs) were 0.95 (95% confidence interval [CI] 0.9-1.0), 1.1 (1.1-1.2) and 1.3 (1.3-1.4) for low, medium, and high intensity of exposure. Corresponding results for probability of exposure were 1.1 (1.0-1.1), 0.9 (0.86-0.94) and 1.2 (1.1-1.2). The risk was higher for squamous cell carcinoma of the lung than for other histological types. Results in women were not suggestive of an effect (RR in the category of medium or high intensity of exposure 1.1, 95% CI 0.6-1.8). A small but significant increase in risk of cancers of the stomach (SIR 1.06), pancreas (SIR 1.05), larynx (SIR 1.09), and the kidney (SIR 1.06) was present among men exposed to diesel emissions, without a clear trend according to either probability or intensity of exposure. The SIR among women was non-significantly increased for stomach, pancreatic, and laryngeal cancers, but not for kidney cancer. Furthermore, a significantly increased risk of oral/pharyngeal (SIR 1.64) and cervical (SIR 1.48) cancers was present among women, with a suggestion of a dose-response relationship. There was no increased risk of bladder cancer in either gender. CONCLUSIONS: The results of this study provide evidence of a positive exposure-response relationship between exposure to diesel emissions and lung cancer risk among men. The positive results for other neoplasms, such as stomach, pancreatic, oral/pharyngeal, and cervical cancers, cannot be attributed to diesel exposure, but they deserve attention in future investigations.