Density functional theory calculations of the relative stabilities of the ortho, meta, and para MClY(XC4H4)(PH3) 2 heterometallabenzenes (M = Rh, Ir; X = N, P; Y = Cl and M = Ru, Os; X = N, P; Y = CO) have been carried out. The ortho isomer is the most stable for X = P, irrespective of the metal M. For X = N and M = Ir, Rh the meta is the lowest-lying isomer, whereas for M = Ru, Os the ortho and meta isomers are almost degenerate. The electronic structure and chemical bonding have been investigated with energy decomposition analyses of the interaction energy between various fragments, to discuss the origin of the differences observed. The values of the multicenter index of aromaticity and nucleus-independent chemical shifts indicate that the heterometallabenzenes studied should be classified as aromatic or slightly aromatic ; We thank the following organizations for financial support: the Ministerio de Ciencia e Innovacion (MICINN, project numbers CTQ2011-23156/BQU, CTQ2011-23441/BQU, and CTQ2011-25086, Ramon y Cajal contract to J.P., and FPI fellowship to M.E.H.), the DIUE of the Generalitat de Catalunya (project numbers 2009SGR637, 2009SGR528, and XRQTC), and the FEDER fund (European Fund for Regional Development) for the grant UNGI08-4E-003. Excellent service by the Centre de Supercomputacio de Catalunya (CESCA) is gratefully acknowledged