Risk of aplastic anemia (AA) from occupational exposures to pesticides and industrial chemicals was evaluated in a hospital-based case control study in Thailand (541 cases of AA and 2261 controls). Exposure data were obtained via participants' self-reports and by experts' assessments and the data from these 2 exposure assessment methods were compared. There was an increased risk of AA associated with several classes of pesticides measured by either self-report or expert assessment. The strongest associations were seen in those whose exposures were identified both by self-report and by expert assessment. Comparing very high/high to no exposure, odds ratios (95% confidence intervals) were as follows: for organophosphates 3.20 (1.87-5.46), carbamates 4.75 (1.92-11.75), organochlorines 6.04 (1.31-27.84), and paraquat 2.17 (1.11-4.25). There were correlations among the pesticides because many types were used in the same job, so it was not possible to determine whether these risks were independent or because of confounding of one by another.