Social media (SM) offers huge potential for public health research, serving as a vehicle for surveillance, delivering health interventions, recruitment to trials, collection of data, and dissemination. However, the ‘networked’ nature of the data is riddled with ethical challenges, and there is no clear consensus as to the ethical handling of such data. The aim of this paper is to outline the key ethical concerns for public health researchers using SM, and discuss how these concerns might be best addressed. Key issues discussed include those of privacy; anonymity and confidentiality; authenticity; the rapidly changing environment; informed consent; recruitment, voluntary participation and sampling; minimizing harm; data security and management. Despite the obvious need, it is difficult to produce a set of prescriptive guidelines for researchers using SM, as the field is evolving quickly. What is clear, however, is that the ethical issues connected to SM related public health research are also growing. Most importantly, public health researchers must work within the ethical principles set out by the Declaration of Helsinki that protect individual users first and foremost.