In the electrophilic addition of bromine to norbornadiene, the intermediate molecular complexes between norbornadiene and bromine have been investigated and their stable configurations determined using AM1 semiempirical method. The geometric parameters and stabilization energies of the complexes have been calculated. The exo and endo adducts are found to be nearly isoenergetic, but an exo selectivity has been observed. The cationic intermediates of the reaction have been studied by ab initio SCF method in STO-3G and STO-3G* basis and also by MNDO semiempirical route. Exo-bromonium cation is found to be more stable than endo-bromonium cation according to both the methods. The results obtained indicate that a multicenter non-classical bromocarbonium cation formed by the rearrangement of exobromonium cation is the most stable one among the cationic intermediates. It is likely that the ionic addition reaction proceeds via the non-classical bromocarbonium ion and results in the formation of,the rearranged products.