For humanitarian health-care practitioners bearing witness to violations of human dignity has become synonymous with denunciations, human rights advocacy, or lobbying for political change. A strict reliance on legal interpretations of humanitarianism and human rights is inadequate for fully understanding the problems inherent in political change. With examples from the HIV/AIDS epidemic in the USA, the Rwandan genocide, and physician-led political activism in Nepal, we describe three cases in which health practitioners bearing witness to humanitarian and human-rights issues have had imperfect outcomes. However these acts of bearing witness have been central to the promotion of humanitarianism and human rights, to the pursuit of justice that they have inevitably and implicitly endorsed, and thus to the politics that have or might yet address these issues. Despite the imperfections, bearing witness, having first-hand knowledge of humanitarian and human-rights principles and their limitations, and systematically collecting evidence of abuse, can be instrumental in tackling the forces that constrain the realisation of human health and dignity.