Despite federal regulations, farmworkers often lack access to basic information about pesticides applied at their worksites. Focus groups revealed that farmworkers have developed an extensive body of lay knowledge, based on personal perceptions, about pesticides and pesticide exposure including means of pesticide exposure, means of pesticide entry into the body, and the potential health effects of pesticide exposure. We describe how this lay knowledge, when combined with technical information that is required to be provided to workers by law, provides valuable data to consider before developing and implementing health interventions designed to reduce the adverse health effects of pesticide exposure.