The most stable structure of the benzene trimer cation was systematically searched using CCSD(T)/6-31G(d)//MP2/6-31G calculations, and several stable structures were obtained. A sandwich structure (SW) is found to be the most stable, though a few other structures have similar energies. Calculated differential spin densities indicate that the positive charge of SW is localized around a dimer core in SW, as suggested from experiments. A calculated infrared spectrum and the low-lying excited states of the obtained stable structures are compared with the experimental results. It is also shown that the core switching of a dimer cation can occur in SW. (c) 2007 Elsevier B.V. All rights reserved.