Using a first principles pseudopotential method we have studied the adsorption of H on the high index Si(1 1 4)-(2 x 1) surface within the local density approximation. This stable surface is found to be both chemically and electronically passivated by two different coverages of hydrogen: 1.0 ML and 1.5 ML. For the 1.0 ML coverage all the A- and B-type dimer bond lengths have equalised to 2.40 Angstrom and the rebonded lengths are slightly longer at 2.48 Angstrom. Hydrogen passivation, for both coverages. leads the surface bands of the clean Si(1 1 4)-(2 x 1) surface to move into the bulk valence and conduction bands. Differences in the density of states for the clean, 1.0 ML and 1.5 ML coverages were observed and are discussed. (C) 2004 Elsevier B.V. All rights reserved.