Accompanied with various opinions across cultures, truth telling is a major debate in bioethics. Many studies have focused on attitudes toward truth disclosure. We intend to review several relevant research studies, and discuss the issue through a clinical case consultation. It seems that while "the right to know" is emphasized in bioethics, in some cultural contexts, health professionals fear communicating bad news. The patients may not receive information directly, because it is believed that the truth may make the patient feel hopeless and unable to cope with the problem. Nevertheless, some believe that sharing information may strengthen a trusting relationship between patients and medical professionals. Extensive efforts are in process in some societies to make patient rights to know the truth as a natural part of medical practice. However, in some cases, the principles of respect for patient autonomy require us to accept patient's refusal to know the truth, with the provision that he assigns someone to receive information and make medical decisions on his behalf. In conclusion, it is suggested that healthcare professionals should not act on a unique presumption in all cases and they should explore what the real interest of patient is, in order to respect individual autonomy.