The principle of respect for autonomy requires informing patients adequately and appropriately about diagnoses, treatments, and prognoses. However, some clinical cases may cause ethical dilemmas regarding telling the truth. Under the existence especially of certain cultural, social, and religious circumstances, disclosing all the relevant information to all pertinent parties might create harmful effects. Even though the virtue of telling the truth is unquestionable, sometimes de facto conditions compel physicians to act paternalistically to protect the patient/patients from imminent dangers. This article, (...) which aims to study the issue of whether a physician should always tell the truth, analyzes an interesting case that represents the detection of misattributed paternity during pre-transplant tests for a kidney transplant from the son to the father in Turkey, where social, cultural, and religious factors have considerable impact on marital infidelity. After analyzing the concept of telling the truth and its relationship with paternalism and two major ethical theories, consequentialism and deontology, it is concluded that the value of the integrity of life and survival overrides the value of telling the truth. For this reason, in the case of a high possibility of severe and imminent threats, withholding some information is ethically justifiable. (shrink)