Pesticide exposures cause disorders varying from straightforward topical irritant reactions, such as those to synthetic pyrethroid insecticides, to complex systemic illness, such as that resulting from cholinesterase inhibition by organophosphate pesticides. The acute illness syndromes associated with pesticides most commonly encountered by clinicians are illustrated here by cases reported to the California Pesticide Illness Surveillance Program. The issues raised include asthma associated with exposure to contaminants in organophosphate insecticides, systemic toxicity of ingested pyrethroids (in children), and illnesses associated with spills or misuse of fumigants.