The veracity of behavioral self-reports is often challenged, particularly when the motivation to avoid stigma and win social approval holds potential to introduce bias into the data collected. This study employed plasma cotinine tests to validate the self-reports of tobacco use collected from 3,841 casino employees as part of a comprehensive health survey. Rates of discordance were calculated by comparing employee self-reports with results from plasma cotinine tests. This study provides evidence that casino employees can provide valid self-report data. Further, discordance rates of self-reported tobacco use vary according to operational definitions of tobacco use. These findings highlight the methodological importance of recognizing the inherent heterogeneity of smoking behavior.