High-level, restricted coupled cluster with singles, doubles, and perturbative triples calculations are performed to determine the ground electronic state of KO. In the absence of spin-orbit coupling, we find that the ground state is a (2)Sigma(+) state, with a (2)Pi state lying just over 200 cm(-1) higher in energy. We ascertain that basis set extension, higher-order correlation energy, mass-velocity, and Darwin relativistic terms do not change this ordering. We then calculate the low-lying Omega states when spin-orbit coupling is turned on. The (2)Sigma(1/2)(+) state undergoes an avoided crossing with the (2)Pi(1/2) state, and we therefore designate the ground state as X-1/2. This state is essentially (2)Sigma(1/2)(+) at short R, but essentially (2)Pi(1/2) at long R; there is a corresponding A 1/2 state with the opposite behavior. These states have significantly different shapes and so spectroscopy from the adiabatic states. Finally, we calculate the dissociation energy D-0, of KO as 66 +/- 1 kcal mol(-1) and derive DeltaH(f) (KO, 0 K) as 13.66 +/- 1 kcal mol(-1).