Imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine, CAS 138261-41-3] belongs to a relatively new class of insecticidal chemistry, the chloronicotinyl neonicotinoid compounds. Animal studies indicate relatively low toxicity to mammals. Despite wide usage in some countries, the understanding of human poisoning is quite limited. Here we report a fatal case of rapid ingestion of an insecticide formulation containing imidacloprid. Clinical manifestation included severe vomiting, hypertension, tachycardia, mydriasis with sluggish reaction to light, and loss of consciousness. In the course of toxicity, the patient manifested bradycardia, bradypnea, and cardiopulmonary arrest and death. Because moderate- to high-dose imidacloprid in animals causes central nervous system activation similar to nicotine, including tremors, impaired papillary function, and hypothermia, it is more likely that the formulation ingredients caused most of the clinical symptoms including central nervous system depression and gastrointestinal irritation.