Forty-two cases of feline permethrin toxicity treated at a referral hospital in Sydney, Australia were retrospectively reviewed. In most cases canine permethrin spot-on (PSO) flea products had been directly applied to affected cats. Most presented during summer and there was an increase in cases during the 2007/2008 period. Clinical signs included; tremors/muscle fasciculations (86%), twitches (41%), hyperaesthesia (41%), seizures (33%), pyrexia (29%), ptyalism (24%), ataxia (24%), mydriasis (19%) and temporary blindness (12%). Treatment involved decontamination, anticonvulsants and supportive care. Methocarbamol was not used. Complications occurred in 33% of cats and included: hypothermia (29%), electrolyte abnormalities (26%), aspiration pneumonia (12%), hypoproteinaemia (12%), anaemia (5%), apnoea (7%), respiratory arrest (5%), cardiorespiratory arrest (2%), pleural effusion (2%), urinary tract infection (2%) and corneal ulceration (2%). One cat was euthanased. Feline permethrin toxicity may result in severe clinical signs requiring intensive treatment. Despite prominent label warnings, cases of feline permethrin toxicity continue to occur in Australia and may be fatal.