The negative hydrogen ion formation process on a cesiated W(110) surface is studied by scattering a proton beam from such a surface. The primary energy ranges from 50 to 3000 eV. The angle of incidence with respect to the surface normal is 45° or 70°. A maximum negative‐ion formation probability of 0.67 is measured. This quantity does not depend on the angle of incidence. However, it is strongly influenced by the time the surface has been exposed to the beam. This effect is attributed to hydrogen implantation.