The theory of atoms in molecules equates the energy of a group to the negative of its electronic kinetic energy, using the atomic statement of the virial theorem. In general, a correction must be applied because of the failure of the wave function to satisfy the virial theorem. This Letter examines the transferability of group energies using self-consistently scaled wave functions that satisfy the virial theorem at both single determinant and correlated levels of theory to demonstrate that apparent deviations in the transferability of the group energies found in certain homologous systems, is an artefact arising from the variation in the virial correction factor. (C) 2003 Elsevier B.V. All rights reserved.