In a medical climate where doctors are usually pressed for time, patients commonly leave their appointments feeling confused, unable to recall what was discussed, or simply missing information. These communication difficulties result in gaps in patients' knowledge about their conditions and their potential treatments. One response to this problem has been that patients join online health communities as a way to access more information and obtain social support. Research shows that participating in these communities has important benefits, including decreased depression, better ability to cope, and increased social networks that can aid in accessing needed information. However, little research addresses the specific information gaps patients experience, how they fill these gaps through online communication, and how online health information behavior interacts with medical decisions and patient-provider communication. Drawing on data from 31 semi-structured, in-depth interviews, participant observation, and online archives analysis, this paper examines the health information interactions that participants in an online breast cancer community experienced as they progressed through breast cancer and survivorship. The findings reveal an extensive array of information that, from the patients' perspectives, was either not communicated or was inadequately communicated during patient-provider interactions. This research highlights patients' perceptions of information gaps, how patients navigated through their information gaps with the help of the community, and the significance of peer interaction in the comprehension of medical information and medical decision-making.