Density functional calculations with the B3-LYP functional were used to optimize the platinum-carbon cationic clusters, PrCx+, 1 less than or equal to x less than or equal to 16, in both the doubler and quartet states of the linear, fan, opec-ring, closed-ring, and one-carbon-ring geometries. Trends in stability, Pt+-C-x binding energy, doublet-quartet excitation energy, and Pt-C bond lengths were investigated. Explanations for these patterns are provided in terms of orbital interactions and changes imposed on the carbon chain by the metal atom. In accord with the previously studied palladium-carbon cations, the PtCx+ clusters favored a linear geometry for 3 less than or equal to x less than or equal to 9. For larger clusters, the open-ring (Pt inserted in C-x ring) and closed-ring (Pt bound to two atoms of closed C-x ring) families exhibit the lowest-energy structures. The stability and the nature of the Pt-C bonding in both the closed-ring and one-carbon-ring (Pt bound to one atom of closed C-x ring) PtCx+ structures depend greatly on the aromaticity of the corresponding C-x ring. However, unlike their palladium counterparts, the closed-ring platinum clusters were found invariably to be more stable than the respective one-carbon species. The stability of forming two Pt--C sigma bonds is due to relatively lower energy sd hybrid orbitals from the platinum cation.