This study was conducted to identify risk factors for paraquat-related occupational illnesses. Pesticide-related illness is a reportable disease in California. A total of 231 skin (26.0%), eye (32.0%), local respiratory (3.5%), and systemic (38.5%) paraquat-related cases were reported to the Worker Health and Safety Branch, California Department of Food and Agriculture, during 1971 through 1985. Following paraquat exposure, we found no cases of pulmonary fibrosis. Annual numbers of cases ranged between 1 and 33 (median = 14 cases/y). Information on illnesses reported during 1981 through 1985 (n = 62) was merged with detailed information on paraquat use in agricultural settings (111,716 applications) for the same years. We found that crop treated, method of application, and season of application all contributed independently to the risk of reported illness. Hand application was associated with a higher risk of illness, compared with air application (RR = 99.1, 95% CI = 22.16-443.47); summer application was associated with a higher risk of illness than was winter application (RR = 4.1, 95% CI = 1.91-8.61); and fruit trees were associated with higher risk of illness than were other crops (mainly cotton) (RR = 3.6, 95% CI = 1.18-11.21).