We propose the design of a dielectric flat lens for visible wavelengths, capable of efficiently focus the incident field at a given distance. Our approach relies on the recently proposed exploitation of high-index dielectric resonators with spectrally overlapping electric and magnetic dipole resonances of equal strength. This allows the design of 'metasurfaces' characterized by a nearly-full transmission and phase coverage of 360°. Our numerical results confirm that this type of lenses is capable to manipulate and efficiently focus light with low absorption losses. Furthermore it is directly integrable into a nanophotonic system, thanks to its low profile compared to traditional lenses.