Objective: Communication technologies, such as personal online health communities, are increasingly considered as a tool to realise patient empowerment. However, little is known about the actual use of online health communities. Here, we investigated if and how patients-use of online communities supports patient empowerment. Setting: A network of primary and secondary care providers around individual patients with Parkinson's disease. Participants: We conducted case studies to examine our research question. We interviewed 18 patients with Parkinson's disease and observed the use of online health communities of 14 of them for an average of 1 year. Primary outcome measures: We analysed the interviews and the online conversations between patients and healthcare providers, using Foucault's framework for studying power processes. Results: We observed that patient empowerment is inhibited by implicit norms that exist within these communities around the number and content of postings. First, patients refrained from asking too many questions of their healthcare providers, but felt obliged to offer them regular updates. Second, patients scrutinised the content of their postings, being afraid to come across as complainers. Third, patients were cautious in making knowledge claims about their disease. Conclusions: Changing implicit norms within online communities and the societal context they exist in seems necessary to achieve greater patient empowerment. Possibilities for changing these norms might lie in open dialogue between patient and healthcare providers about expectations, revising the curriculum of medical education and redesigning personal online health communities to support two-way knowledge exchange.