To investigate the elementary events of the decomposition of transition metal complexes, a density functional study of the systems Cr(C6H6)(2) and Cr(C6H6) as well as their corresponding cations, has been carried out. The results give a low bond energy (0.36 eV) for the neutral CT(C6H6) compound while the binding energy of the cation Cr(C6H6)(+) is much higher (1.84 eV), in good agreement with previous theoretical and experimental studies. Concerning the dissociation of Cr(C6H6)(2), the first process (dissociation of the first ligand) needs much higher energy than the second one, and depends on the intersystem crossing relaxation (ISC) of the intermediate Cr(C6H6) compound. Taking into account the ISC process, the three-body decomposition occurs at 3.40 eV, in good agreement with recent experimental results. In the case of the Cr(C6H6)(2)(+) dissociation, both processes (with and without ISC) may be available from recent experimental works. Our theoretical results reproduce very well the values corresponding to both ways of decomposition.