Science is difficult for even its researchers to understand. Science journalists must understand scientific discoveries well enough to write clear, accurate explanations of scientific discoveries for laypeople. A sense of ethical judgment will help journalists ensure that their accounts are reliable and appropriate. Responsible science journalists will maintain a working knowledge of statistics so they can accurately present the statistical aspects of scientific studies. Also, the traditional emphasis on fairness and balance in news coverage may backfire in science reporting, when equal coverage for unreliable “sides” of an issue would in fact be inaccurate. Not all sources are equally reliable; information from peer-reviewed journals, researchers and press officers, while all useful, should be treated with different degrees of caution. These principles of responsible science journalism are shown in three case studies of pharmaceutical debates in the mass media over the past twenty years: the question of whether the MMR vaccine causes autism, the benefits and risks of postmenopausal hormone replacement therapy, and the hazards of the fen-phen diet drug.