Occupational exposure to wood dust is one cause of nasopharyngeal cancer (NPC); however, assessing thisexposure remains problematic. Therefore, the objective of this study was to develop a semi-quantitative exposureassessment method and then utilize it to evaluate the association between occupational exposure to wood dust andthe development of NPC. In addition, variations in risk by histology were examined. A case-control study wasconducted with 327 newly diagnosed cases of NPC at the National Cancer Institute and regional cancer centersin Thailand with 1:1 controls matched for age, gender and geographical residence. Occupational informationwas obtained through personal interviews. The potential probability, frequency and intensity of exposure towood dust were assessed on a job-by-job basis by experienced experts. Analysis was performed by conditionallogistic regression and presented in odds ratio (ORs) estimates and 95% confidence intervals (CI). Overall, a nonsignificant relationship between occupational wood dust exposure and NPC risk for all subjects was observed(ORs=1.61, 95%CI 0.99-2.59); however, the risk became significant when analyses focused on types 2 and 3 ofNPC (ORs = 1.62, 95%CI 1.03-2.74). The significant association was stronger for those exposed to wood dust for> 10 year (ORs=2.26, 95%CI 1.10-4.63), for those with first-time exposure at age > 25 year (ORs= 2.07, 95%CI1.08-3.94), and for those who had a high cumulative exposure (ORs=2.17, 95%CI 1.03-4.58) when compared withthose considered unexposed. In conclusion, wood dust is likely to be associated with an increased risk of type 2or 3 NPC in the Thai population. The results of this study show that semi-quantitative exposure assessment issuitable for occupational exposure assessment in a case control study and complements the information fromself-reporting.