PURPOSE:Online communities have been heralded as one of the most promising health resources on the Internet. The purpose of this study was to identify the characteristics and levels of use of online communities for breast cancer survivors. METHODS:Using Google, we identified websites with a string of computer-mediated communication terms and individual queries of three to five words of online community terms. This was complemented by a review of website resource lists and personal libraries. Two reviewers independently extracted information on their general characteristics and number of members and message board posts. A coding scheme guided content analysis. RESULTS:We found 111 websites. Most sites (n = 64, 65.8 %) had a broad focus (e.g., health, cancer, or general). One third (n = 38, 34.2 %) were exclusive to breast cancer and 11 catered to specific disease characteristics. The majority were American (n = 79, 75.2 %), nonprofit (55.0 %), and moderated (69.5 %). Most moderators (85.7 %) were staff or community members; eight sites were moderated by health professionals. Greater than one-third of sites (n = 40, 36 %) were initiated by breast cancer survivors or loved ones. Breast cancer-specific sites contained a total of 4,186,275 posts. One-third (n = 10) contained 93.4 % of posts, displaying over 100,000 posts each. As of April 3, 2012, eight sites were discontinued. CONCLUSIONS:There is a wide range of online communities available for breast cancer survivors with extensive archives of personal illness experiences. Future efforts should focus on identifying the factors that determine their success and effectiveness.