The electronic bandstructure of an ordered 1*1 overlayer of Sb on InP(110) has been investigated by angle-resolved photoelectron spectroscopy using synchrotron radiation. The experimental energy dispersion of the features in the spectra has been mapped along high-symmetry directions in the surface Brillouin zone. An analysis based on a number of criteria is employed to distinguish surface-related features and these are compared with a 'tight-binding, total energy minimization' calculation based on a zig-zag chain model of Sb on the InP(110) surface. Two bands near the valence band maximum are found to be in reasonable agreement with predicted states with a bonding character associated with the adsorption on anion and cation sites. The nature of two further bands at higher binding energy is discussed.