The purpose of the severity index is to provide simple, standardized criteria for assigning severity to cases of acute pesticide-related illness and inj ury. It is important to assign a severity category to each case of acute pesticide-related illness and injury. An understanding of illness severity will be useful for evaluating the morbidity of acute pesticide-related illness and injury, for assessing its impact on society, and to assist the targeting of limited intervention/prevention resources toward the most pressing pesticide problems. This severity index is based upon existing systems for ranking severity of poisonings, including pesticide illness. It takes into account the following: signs and symptoms; whether medical care was sought; whether the individual was hospitalized; and, whether there was lost time from work or usual activities. Severity should only be assigned to acute pesticide-related illnesses or injuries classified as definite, probable, possible, or suspicious. As such, this severity index should be used in conjunction with the Case Definition for Acute PesticideRelated Illness and Injury Cases Reportable to the National Public Health Surveillance System.