Huge numbers of structures, 7000 isomers and 26229 transition structures, have been searched for C6H6 in quantum chemical calculations by using a GRRM/SCC-DFTB program. The stability of benzene is outstanding. At B3LYP/6-311G(d,p) level, no isomers are found in a wide energy range of 260 kJ mol(-1) above the energy of benzene, except for fulvene at 148 kJ mol(-1). Other isomers are distributed between 260-1250 kJ mol(-1). Thirty experimentally known isomers are found in the energy range below ca. 600 kJ mol(-1).