Single‐crystal gold films were grown by vacuum deposition on heated (375°C) sodium chloride substrate blanks. Completely oriented films with thicknesses between 1000 and 3000 A were obtained, with the plane of the film being the {100} crystallographic plane. A small hole was drilled through the substrate with a water jet, and the mechanical properties were determined by stressing the unsupported film over this hole. The films were observed to undergo considerable plastic deformation, accompanied by the appearance and growth of mechanical twin bands as the stress was increased. X‐ray diffraction studies were made to determine the twin orientation. Both the ultimate tensile stress and the elastic modulus were found to increase as the thickness of the films was reduced.