This paper examines rationales and policies developed by physicians through history about what to tell patients found to have serious illness. The widespread belief among doctors that the revelation of threatening news causes patients considerable anguish and seriously erodes the prospect of maintaining their hope encouraged a policy of concealment for many centuries. Arguments that encourage candor have been increasingly pressed during the last two centuries. Advocates point out that candor can be beneficial and is favored by many patients, and that a policy of concealment usually fails to work, tends to place stress on patients by constraining discussion of anxieties generated by vague or explicit knowledge of the true situation, and exerts a damaging effect on trust in the medical relationship. Not only the moral aspects of this problem but also its clinical dimensions, such as mastering the skill to discuss threatening news with patients, bear considerable scrutiny by physicians and medical educators.