The regulation of the will of the patient expressed in advance is controversial and insufficient in the Latvian legislation. The legal regulation on the will of the patient expressed in advance stipulates clearly only the form of the will of the patient; it has to be established without sufficient reference to its legally binding force. The aim of the research is to carry out a legal analysis of the institution of the patient’s will expressed in advance, to identify legal flaws related to it and to propose particular solutions to eliminate the identified limitations. To achieve the aim, the following research tasks are set: 1) to analyze the legal nature of the patient’s will expressed in advance; 2) to explore the content and term of the patient’s will expressed in advance; 3) to assess the establishment of the patient’s will expressed in advance and its termination. The following research methods are used in the research: semantic method, grammar method, historical method, analytical method, comparative method, systemic method, teleological method. In a result of the research the author has formulated the principles of the will of the patient expressed in advance that could be introduced in the legal regulation on the issue, thus improving the legal protection of the patient. Analysing the legal nature of the patient’s will expressed in advance and taking into account its peculiarity, the content boundaries of this particular type of the expression of the patient’s will were defined identifying the extent of the patient’s self-determination. Assessing various possibilities of choosing the term defining the patient’s will expressed in advance, the author has sustained the most appropriate version of the term considering both national and international legal regulation, and notions of the legal doctrine. Another issue of a similar significance that was analysed in the research were the methods used in the legal practice of the world countries to determine the patient’s will expressed in advance; the author has analysed and offered the determination method, which is the most appropriate for the legal system of Latvia. In the conclusion, types of termination of the patient’s will expressed in advance and their legal consequences were analysed. Furthermore, the author proposes an applicable project of the amendments to the legal regulations in order to implement the theoretical conclusions of the research related to the patient’s will expressed in advance into the legal system of Latvia.