The article talks about the ethical dilemmas of diagnostic and prognostic disclosure in oncology. Below, we discuss the principles of diagnostic and prognostic disclosure to curable and terminally ill patients proposed by Soviet medical deontology. Despite its evolution, the principle of benevolent deception applied to incurable patients in the USSR still persists into the present. The article discusses the cons and pros of withholding the diagnosis from terminally ill patients and the Russian legislation on the patient’s rights. The article places a special focus on the strategy of disclosing an unfavorable diagnosis to a cancer patient adopted in Russian oncology.