Organophosphorus pesticides are widely used as insecticides all over the world because it possesses high biocidal activity. Currently organophosphorus insecticides enhanced usage in agriculture and public health has resulted in environmental pollution and can exert significant adverse effects in non-target organism including the mammalian species. This has increased concern of the consequence of organophosphorus pesticides to the environment. The majority of organophosphorus insecticides exert cholinergic toxicity in human, by phosphorylation of acetylcholinesterase and they are also classified as acetylcholinesterase insecticides. However, some have been shown to cause delayed polyneuropathy which is initiated by the attack on the neuropathy target esterase which is distinct from acetylcholinesterase. The currently investigated continuing issues of organophosphorus pesticides toxicology which includes; common mechanism of action; organophosphorus ester induced delayed neuropathy and risk assessment are discussed.