IN 1959, A RURAL COUPLE TOOK THEIR 9-MONTH-OLD SON, “JOHN,” TO BE tested for something they had never heard of before, hemophilia. They had just read an article about the disease in Reader’s Digest and wondered if John’s bruising and listlessness could be explained by the unfamiliar bleeding disorder. Soon thereafter, John was diagnosed with hemophilia A, a coagulation defect that required countless doctor visits and painful bleeding crises throughout his childhood. While John was in his 20s, the first report about an unusual disease affecting homosexual men appeared in the scientific literature. Later identified as the disease caused by the human immunodeficiency virus (HIV), AIDS has since received tremendous mass media coverage. Perhaps partly as a result of how AIDS was depicted in the press, patients with hemophilia and other groups associated with HIV became modern-day pariahs among some members of the public, who responded with fear and discrimination against them. John, who eventually tested positive for HIV, entertained the idea of submitting a more detailed account of his experiences for this issue of MSJAMA. However, 20 years after AIDS first hit the press, John decided that publishing his story would invite unwelcome scrutiny of him and his family, especially by those in his community who still live in irrational fear and ignorance of the transmissibility of HIV. This true story illustrates the enormous impact—both positive and negative—that magazines, television, radio stations, daily newspapers, and other communication entities that comprise the “mass media” can have on an individual’s health and life. Every day, physicians face the myriad effects of the mass media on their patients’ perceptions of health care and medical science. This issue of MSJAMA explores some challenges and opportunities that arise as a result of disseminating scientific and medical information to the public. To better understand how the mass media shapes the public’s perception of medicine, it is important to quantify the public’s response to media coverage and critically analyze the contents of this coverage. Gail Geller, Barbara A. Bernhardt, and Neil A. Holtzman discuss the mass media’s role in influencing the public’s perception of genetics research. Lisa Schwartz and Steven Woloshin lend a critical eye to the health claims made in some medical advertisements. While misrepresentation of medical information by mass media can have negative consequences, the use of mass media to educate the public about medicine has an enormous potential to do good. Physician and reporter Miriam Shuchman discusses examples of good reporting that has resulted in positive changes in the health care field.