The Proceedings of the 4th Brazilian Workshop on High Performance Computing Systems (WSCAD 2003) bring the papers selected and presented in the edition of the event held in São Paulo/SP, from November 10 to 12, 2003. In this issue, the proceedings include 19 full papers. These papers were selected through a peer-review, from a total of 57 full papers submitted, which implied an acceptance rate of 33,3%. The event's program committee was coordinated by Carlos Augusto Paiva da Silva Martins (PUCMG) and Wagner Meira Jr. (UFMG), who organized this volume.