Earlier calculations on (100) high-angle twist boundaries in Al are extended to Cu, Ag and Au. Recent pseudopotentials of Dagens together with three empirical potentials for Cu are applied. Boundaries with values of Σ, the inverse density of coincidence sites, ranging between 5 and 73 are considered. In contrast to our earlier results for the Al pseudopotential of Dagens et al., the relaxed grain-boundary energy, E Σ , is found to increase smoothly as function of the twist angle, θ, for all six potentials considered here; i.e. “cusps” in the E Σ ( θ) curve are not observed. Rather similar boundary structures are obtained for the noble-metals; these differ drastically from those derived by means of the pseudopotential for Al. From a comparison with (100) twist boundaries in ionic crystals with NaCl structure it is concluded that also in the f.c.c. metals a volume expansion at the interface which increases smoothly with θ should be present. Interfacial structures determined without consideration of this expansion are hence concluded to be systematically in error. The article concludes with a summary of the properties of (100) twist boundaries in the f.c.c. and NaCl structures which are thought to be valid independent of the detailed form of the interatomic potential chosen.