This hybrid review-case study introduces three-dimensional (3-D) virtual worlds and their educational potential to medical/health librarians and educators. Second life (http://secondlife.com/) is perhaps the most popular virtual world platform in use today, with an emphasis on social interaction. We describe some medical and health education examples from Second Life, including Second Life Medical and Consumer Health Libraries (Healthinfo Island-funded by a grant from the US National Library of Medicine), and VNEC (Virtual Neurological Education Centre-developed at the University of Plymouth, UK), which we present as two detailed 'case studies'. The pedagogical potentials of Second Life are then discussed, as well as some issues and challenges related to the use of virtual worlds. We have also compiled an up-to-date resource page (http://healthcybermap.org/sl.htm), with additional online material and pointers to support and extend this study.