Helium diffraction data and corrugation parameters for a (1 × 1) chemisorbed layer of hydrogen on the Pt(111) surface have recently been reported by Lee et al. We have calculated the corrugation parameters using a first principles approach and conclude (in agreement with Lee et al.) that H chemisorbs in a three fold site. Furthermore we establish that the vertical height of the H above the top plane of Pt atoms is about 1 Å. Also by combining our results with the experimental helium diffraction and X-ray data of Lee et al., we confirm their tentative suggestion that the H adsorbs in a hcp type three fold site. © 1984.