The ground and low-lying electronic states of the 1,3,5-tridehydrobenzene triradical are characterized by electronic structure calculations. It is found that the ground state is the (2)A(1) doublet of C-2v symmetry. Another doublet state lies 0.1-0.2 eV higher in energy, and the lowest quartet state of D-3h symmetry is 1.2-1.4 eV higher in energy. Both doublets are degenerate at D-3h geometries and undergo different Jahn-Teller distortions. Structurally, the triradical is tighter than the parent neutral molecule (benzene), because the interaction among the unpaired electrons results in additional bonding even in the high-spin state (quartet). The adiabatic doublet-quartet energy gap and the excitation energies calculated at the equilibrium geometries of the 3,5-dehydrophenyl anion are provided to aid in the design and interpretation of photoelectron experiments. (C) 2003 American Institute of Physics.