Abstract: Disclosed herein is a cosmetic composition for treating keratin fibers, for example human keratin fibres such as the hair, comprising, in a cosmetically acceptable medium, at least one anionic fixative polymer comprising as monomers at least a vinyl lactam, an ethylenically unsaturated carboxylic acid, and an acrylate chosen from alkyl acrylates and alkyl methacrylates whose alkyl moiety contains at least 6 carbon atoms, and at least one surfactant chosen from ionic and nonionic surfactants; wherein the composition has a viscosity greater than 2 poise (200 cps) at 25° C. at a shear rate of 1 s?1.