Full hemispherical X-ray photoelectron diffraction (XPD) experiments have been performed to investigate at the atomic level ultrathin epitaxial c-axis oriented PbTiO3 (PTO) films grown on Nb-doped SrTiO3 substrates. Comparison between experiment and theory allows us to identify a preferential ferroelectric polarization state in a 60 angstrom - thick PTO film. Multiple scattering theory based on a cluster-model [Phys. Rev. B 63, 075404 ( 2001)] is used to simulate the experiments.