Objectives: To assess the relationship between occupational exposure to metalworking fluids (MWFs) in the steel-producing industry and bladder cancer incidence. Methods: A nested case–control study on bladder cancer was set up in a cohort of workers from six French steel-producing factories. Three controls were randomly selected for each incident bladder cancer case diagnosed from 2006 to 2012. Controls were matched to cases on age at diagnosis and counter-matched on a surrogate measure of exposure to MWFs derived from a job-exposure matrix. Cases (n=84) and controls (n=251) were face-to-face interviewed. Experts assessed occupational exposure to MWFs (straight, soluble and synthetic) using questionnaires and reports from factory visits. Occupational exposures were based on three metrics: duration, frequency-weighted duration and cumulative exposure index. Conditional multiple logistic regressions were used to determine ORs and 95% CIs, taking non-occupational and occupational exposure into account.Results: In the 25 years before diagnosis, ORs increased significantly with duration of exposure to straight MWFs (OR=1.13 (1.02–1.25)) and increased with frequency-weighted duration of exposure to straight MWFs (OR=1.44 (0.97–2.14)). These results remained valid after adjusting for duration of smoking, average number of cigarettes smoked per day, time since smoking cessation and exposure to polycyclic aromatic hydrocarbons (PAHs). ORs also increased with soluble MWFs but not significantly. No significant association was found with older exposures to MWFs or with exposure to synthetic MWFs. Conclusion: The increased risk of bladder cancer observed among workers exposed to straight MWFs and to a lesser extent to soluble MWFs may be explained by the presence of carcinogens (such as PAH) in mineral oils component of straight and soluble oils. Prevention therefore remains necessary in sectors using MWFs.