A Letter by Pendas, Blanco and Francisco [A.M. Pendas, M.A. Blanco, E. Francisco, Chem. Phys. Lett. 417 (2006) 16] recently appeared in this journal whose purported purpose was to present 'A simplified derivation of the variational nature of the real space basins used in the quantum theory of atoms in molecules (QTAIM)...' The purpose of this note is to point out that in their attempt to do so, the authors make a fundamental error. (c) 2006 Elsevier B.V. All rights reserved.