Structural and energetic properties are predicted for the six tridehydropyridinium cation isomers in their lowest-energy doublet and quartet states by using density functional, multireference second-order perturbation, and coupled-cluster theories. Doublet-quartet splittings and triradical stabilization energies are examined to gain insight into the degree of interaction between the three radical centers, with comparison being made to analogous tridehydrobenzenes.