This case study describes the effects of using a Web Based Social Network (WBSN) approach to Knowledge Management in a Brazilian software development organization. During this work it was verified how the previous approach to Knowledge Management, a wiki based approach, did not work to this organization and how users voluntarily migrated from this environment to the WBSN. In addition to the WBSN environment, a Knowledge Management process has been proposed, with some metrics related to its phases. These metrics have been monitored since October 2006 and analyzed in order to verify the efficiency of this approach. In order to give a better understanding of the concepts related to Social Networks and Knowledge Management, it is presented a brief introduction to each one of them, including an evaluation of existing Knowledge Management approaches.