In California, suspected pesticide and work-related illnesses and injuries are reportable conditions. The Occupational Health Branch (OHB) of the California Department of Health Services (CDHS) conducts surveillance of work-related pesticide illness with support from the National Institute for Occupational Safety and Health (NIOSH) and the U.S. Environmental Protection Agency (EPA). On May 12, 2005, CDHS received a report from the California Department of Pesticide Regulation (CDPR) of a suspected pesticide incident in Kern County involving 27 farmworkers (age range: 21--61 years; median: 32.5 years) and six emergency responders (age range: 28--51 years; median: 33.5 years). CDHS investigated this incident by conducting a site visit; reviewing medical and meteorologic records; and interviewing affected workers, pesticide applicators, and the farmworker employer. Findings indicated that workers became ill from drift of a pyrethroid pesticide (cyfluthrin) that was being applied in a neighboring field. Pyrethroid pesticide applicators should always operate in a manner that ensures workers are not exposed.