The electronic structure and the stability of hydrogen-terminated graphene nanoribbons (GNRs) are evaluated by means of gradient-corrected density functional theory calculations and rationalized by application of Clar's theory of the aromatic sextet. Our results show that the electronic properties of GNRs are deeply related to the description of the bonding pattern provided from the valence bond picture obtained by application of Clar's theory. This finding applies either to zigzag-, armchair- and chiral-terminated GNRs and can be expected to have strong impact in the interpretation of experiments and on the design of devices based on nanostructured graphene materials. (C) 2008 Elsevier B.V. All rights reserved.