Environmental tobacco smoke (ETS) is an occupational carcinogen. Large companies often examine ETS exposure by employee surveys. However, reliable and valid self-report measures have been lacking. This study compared validity and reliability of various self-report measures. One hundred and seven nonsmokers from 11 Dutch worksites were interviewed. Three self-report measures were correlated with nicotine concentrations collected with area monitors in nonsmokers' offices. Nicotine concentrations averaged 12.7 micrograms/m. The item "How much tobacco smoke, on average, is there during a day in your work office?" correlated highest with nicotine concentrations (r = 0.65; P < 0.001) and produced the lowest standard error of measurement. It was concluded that this simple self-report item may be a valid measure to assess the reach and effectiveness of worksite smoking policies.