The topic of happiness is one of the oldest in philosophical researches. Now it is the subject of interest, in particular, for bioethicists, scientists who are looking for the principles of proper treatment of human life, health, and death. The concept of happiness acquires special significance in the quality of life bioethical conception. The author of the article outlines the origins of the understanding of happiness adopted by the supporters of this conception, as well as gives examples of its application by them (above all by P. Singer, L. Nordenfelt, and J. McMahan). The quality of life bioethical conception adopted utilitarian vision of happiness, developed mainly by J. Bentham and J. S. Mill. According to it, happiness is identified with benefit or pleasure, which can be measured and maximized. In the XX century utilitarians began to consider autonomy – the ability of a person to manage his or her own life and death – as an important element of happiness. The influence of the preference utilitarianism is also noticeable. In obedience to it they see happiness in the ability of person to realize his or her rational and autonomous desires. The medical conditions that does not allow it are interpreted as lack of happiness. Thus, they justify not only the admissibility of withdrawing treatment that doesn’t give the expected result, but also of euthanasia. Killing a person, in terms of the quality of life conception, may not be a lack of happiness if the other alternative is to continue living in conditions that do not allow a person to realize his or her preferences, or does not coincide with his or her ideas of a decent life. The lives of persons who do not manifest rationality and autonomy are interpreted as inhuman, as wrongful, and the person as deprived of the right to happiness. Critics of the quality of life conception point to the subjectivity of the criteria by which happiness is measured. The second reproach is the reference to the absence of a hierarchy of values. That is why they give pleasure and absence of suffering too much importance.