This research-in-progress is an in-depth case study of the patterns of interactions between participants in a virtual community. The study will examine the stability of the community membership, posting behavior of the members over time, the existence of clusters or groups of users, especially a core group, and the possible classification of members based upon participation. Social network analysis diagrams showing who is talking to whom will be produced, revealing the social structure of the community. All 16,112 messages posted by 1,670 users of a medical virtual community were gathered over the course of one year. Preliminary results are given and future analysis of the data is proposed.