A large set of electronic states of scandium dimer has been calculated using high-level theoretical methods such as quantum diffusion Monte Carlo (DMC), complete active space perturbation theory as implemented in GAMESS-US, coupled-cluster singles, doubles, and triples, and density functional theory (DFT). The ³Î£_u and ⁵Σ_u states are calculated to be close in energy in all cases, but whereas DFT predicts the ⁵Σ_u state to be the ground state by 0.08 eV, DMC and CASPT2 calculations predict the ³Î£_u to be more stable by 0.17 and 0.16 eV, respectively. The experimental data available are in agreement with the calculated frequencies and dissociation energies of both states, and therefore we conclude that the correct ground state of scandium dimer is the ³Î£_u state, which breaks with the assumption of a ⁵Σ_u ground state for scandium dimer, believed throughout the past decades.