Permethrin is a pyrethroid insecticide used in dermally applied spot-on flea treatments for dogs. Permethrin-based spot-on preparations are contraindicated in cats because of the high risk of toxicosis. The Veterinary Poisons Information Service (VPIS) is a 24-h access telephone service that provides veterinary professionals in the United Kingdom with information on the management of poisoned animals. In a review of 286 cases reported to the VPIS regarding inappropriate feline exposure to permethrin spot-on (PSO) preparations, 96.9% were symptomatic. Increased muscular activity (as evidenced by twitching, tremor, muscle fasciculations or convulsions) was common and occurred in 87.8% of cases. The duration of increased muscle activity was long, with convulsions lasting on average 38.9 h and tremors 32 h. Recovery typically occurred within 2 to 3 days but in some cases took 5 to 7 days. Death occurred in 10.5% of cases.