This article reviews the current knowledge about cosmic rays and their possible effects on health of air crew, discusses research directions necessary for establishing and measuring the risks, and highlights the need for physicians and air crew to be informed, despite the inconclusiveness of the evidence. A literature review of computerised medical and scientific databases was carried out. Recent reports highlighting increased incidence of cancer among airline pilots and cabin crew have renewed concerns about possible exposure to harmful levels of cosmic radiation at altitude. Such low energy ionising radiation has been shown to cause double stranded DNA deletions and induce genomic instability in human chromosomes. In the field of microelectronics, cosmic rays have been shown to cause “hard” and “soft” errors in computer microchips, in a dose-response fashion with increasing altitude. Pregnant cabin crew members are of special concern. Although the epidemiological evidence is still inconclusive, we know enough to warrant a cautionary stance. The European Union (EU) leads the way in legislation.