(Chemical Equation Presented) The stereoselectivity-determining oxidative addition step in the Suzuki-Miyaura cross-coupling of α-bromo sulfoxides is analyzed computationally through DFT calculations on a model system defined by Pd(PMe3)2 and CH3SOCH2Br. Both monophospine and bisphosphine complexes have been considered, different reaction pathways being characterized through location of the corresponding transition states. The lowest energy transition states correspond to nucleophilic substitution mechanisms, which imply inversion of configuration at the carbon, in good agreement with experimental data on the process. The energy-lowering and stereodirecting role of the sulfinyl substituent is explained through its attractive interactions with the palladium center, which are only possible in the most favored mechanisms. © 2009 American Chemical Society.