Dichlorvos, 2,2-dichlorovinyl dimethyl phosphate, an organophosphate insecticide, is widely used for the control of agricultural, industrial, and domestic pests (Fig. 1) . Dichlorvos is administered orally as an anthelmintic to swine, horses, cats, and dogs. It is applied by dermal application to cattle, goats, sheep, swine, and chickens to control fleas, flies, and mites. Cucumbers, radishes, lettuce, and tomatoes are treated with dichlorvos in greenhouses. Aerosols and strips are used for the control of ants, bedbugs, ticks, cockroaches, flies, mosquitoes, silverfish, spiders, and wasps. Exposure to dichlorvos is by the inhalation of sprays or vapors from impregnated resins, by skin contact, or orally as a residue in food. The predominant mode of toxicity of dichlorvos is inhibition of cholinesterase. This review includes, to the best of our knowledge, every study on the carcinogenicity of dichlorvos in animals. The studies reviewed are: NCI Dichlorvos Rat Study, Tunstall Laboratory Dichlorvos Rat Study, Kettering Laboratory Dichlorvos Rat Study, Kettering Laboratory Dichlorvos Dog Study, Shell Chemical Company Dichlorvos Swine Study, and NCI Dichlorvos Mouse Study. The conclusions from the NCI Dichlorvos Rat Study and the NCI Dichlorvos Mouse Study are based on my examination and diagnosis of the histological sections. Statistical tests of significance were obtained with Fisher's exact test, and tests for positive linear trend and departure from linear trend.