Aqueous solutions of an oligo(ethylene oxide)-n-perfluorooctyl ether with an average number of 16 ethylene oxide groups (abbreviated CFEO(16)) were investigated. The phase diagram in the temperature composition plane qualitatively corresponds to the general behavior observed for oligo(ethylene oxide)-12-alkyl ether/water mixtures. A series of light-scattering studies on isotropic solutions reveals enhanced scattered intensity with increasing temperature. Small angle neutron-scattering (SANS) experiments show this to be due to anisotropic micellar growth.