Permethrin is a synthetic pyrethroid insecticide commonly used on pets. This compound affects insects by reversibly altering the activity of nerve sodium ion channels and is often one of the active ingredients in "dogs only" spot-on products. In general, toxic effects are not observed in mammals because it is rapidly metabolized by the liver via hepatic glucuronidation. Cats are more sensitive to permethrin compared to other species due to their inefficiency in eliminating compounds via this pathway. Clinical signs of permethrin toxicosis include hypersalivation, paw flicking, ear twitching, hyperesthesia, vomiting, diarrhea, depression, ataxia, muscle tremors, seizures, and death. Treatment ranges from no treatment, support care, to seizure control. Misuse of concentrated permethrin spot-on products on cats results in substantial morbidity and mortality. This type of toxicosis is preventable if owners are educated by veterinarians in the potential for severe consequences of permethrin exposure, primary or secondary, in cats.