In Australia and New Zealand, triflumuron (CAS name: 2-chloro-N-[[[4-(trifluoromethoxy) phenyl] amino] carbonyl] benzamide) is commonly used in sheep backline pour-on products for treating sheep biting louse (Bovicola ovis) infestations. To our knowledge, benzoylurea derivatives have not been evaluated for efficacy against W. equi. The aim of this study was to determine the louse control efficacy and dermal safety of triflumuron when applied as a backline pour-on to horses.