The influence of presence on users attitudes and behavior is widely reported in the literature. However, we still lack a good understanding of the effects of system design on the formation of a sense of presence in computer-mediated environments in general and virtual communities in particular. In this research, we address this void. More specifically, we examine the relationship between important system design characteristics and perceived presence. We adopt a multidimensional conceptualization of presence, distinguishing between telepresence and social presence. Deviating from the virtual reality literature, we apply new frameworks for the conceptualization of the main determinants of presence (i.e., interactivity and vividness) that are more relevant to the virtual community context. An empirical study involving 149 members of a virtual community specializing in health issues provided strong support for our model. Vividness and interactivity are found to be significant determinants of both telepresence and social presence. While the role of vividness is more important for social presence, that of interactivity is more important for telepresence. All interactivity dimensions (i.e., active control, communication, and synchronicity) are found to be significant for telepresence. For social presence, however, synchronicity does not seem to be as important as the other interactivity dimensions. The theoretical and practical implications of these results are discussed.