Purpose: A multi-centre IARC-coordinated European cohort study provided evidence of an association between lung cancer risk and bitumen fume exposure. Sensitivity analyses were conducted to assess whether these associations were robust to assumptions in the exposure assessment for which support could not be obtained due to lack of either measurements or direct observations. Methods: New exposure estimates were generated by changing assumptions on exposure levels, specific tasks, lags, and coal tar use. Subsequently, Poisson regression models estimated relative risks (RRs); change in fit of models was evaluated. Results: The influence of these assumptions was minimal, with log-likelihood deviations between -5.0 and 4.7% and similar patterns in dose-dependent increases of lung cancer risk. In the highest exposure categories, point estimates of RRs ranged 2.07-2.83 for average, and 1.22-2.23 for cumulative exposure. Conclusions: The small increase in lung cancer risk associated with bitumen fume exposure depends only to a limited extent on the subjective judgments made in the exposure assessment for this cohort. © Springer-Verlag 2008.