Truth telling is an essential part of current medical practice because of the patient-centered concept and the respect of patient autonomy. Truth telling is also a crucial step in developing "trust" and a good doctor-patient relationship, which is important for successful treatment. It is a duty of the physician to tell the "truth" and let the patients take a central part in their own treatment process. However, telling the truth may sometimes do harm to the treatment process or to the doctor-patient relationship. In some cases, the physician may fall into a troubled situation with the patient or relatives, and incur anger or prosecution because of telling the truth. Therefore, a proper and effective truth-telling process is as important as the "truth" itself for clinical management. The physician needs to learn and to practise the right way to tell the truth in order to achieve the treatment goals.