A medical information system is a ramified information network, which with the help of computer technologies covers and connects all components of the health care sphere on the scale of an institution, region or even country. The first ones were used to optimize simple but time-consuming operations - patient registration and accounting, appointments and financial calculations. Modern systems automate the entire process of clinical management, take on much of the burden of maintaining medical records and patient records, and simplify interaction with government agencies, insurance and social services. The second approach determines the types of information systems applicable to the existing structure of the healthcare industry, and their purpose. According to this approach, there are four organizational levels: basic, institutional, territorial and national. The basic level is the information systems that doctors use in their daily practice. They provide information, reference and expert support for medical activity. It also includes equipment for diagnostic and laboratory tests, therapeutic influence and automated working places of specialists. Institution levels are designed for use in various medical organizations. They include modules for consulting doctors in the diagnosis and treatment of patients, databases on the number and composition of clinic employees, the address list of the population, their medical records, screening and prevention systems. The information systems of research enterprises and specialized educational institutions also belong to this group. Territorial ones perform a management function at the regional level, and state or federal ones work at the national level. The purpose of their implementation is to simplify routine work of a specialist, delegating part of medical operations to a computer program. To improve the quality of medical care in places where there is a personnel shortage or an increased load on the existing specialists. On this basis, four groups of subsystems are distinguished within the basic MIS. Each of them solves a certain problem. Probabilistic systems are based on the statistics, which determine the degree of confidence of an event - a priori (according to the results of all available sample data) or personal, and on this basis they derive a conditional probability of a particular disease. Expert systems are a type of artificial intelligence technology. Whereas probabilistic systems are based on dry statistics, expert systems are based on professional experience. Their creation is an attempt to reproduce a doctor's decision algorithm using computer technology. Medical device-computer systems are a set of equipment for carrying out diagnostic and therapeutic procedures. The peculiarity of this group of basic - direct contact with the patient's body or his/her biological material. They consist of three main blocks: The hardware part is the external technical devices. This includes a variety of sensors, electrodes, emitters, analyzers, as well as computers and microprocessors for information processing and calculations. Software is the "brain" of the hardware. The software defines the devices' functionality, methods and algorithms of their operation, and sets the user interface. The medical part is the knowledge base of the professional field: what the devices do and why, and what the result should be. Device-computer systems are widely used in functional and laboratory diagnostics, patient monitoring, working with medical images, providing therapeutic effect, as well as for compensation of vital functions of the body and prosthetics. The last group, the automated physician workstation. This is the basic unit of the digitalization of the medical sector. The general purpose of APMs is to manage the information that forms the basis of each particular specialist's work. Management means receiving and entering data, their storage, processing (analysis), and, if necessary, searching and distributing. Thus, all groups of basic MIS described above must have integration with automated workstations. Automated workstations for physicians are used both on the basic level and on the level of medical institutions. Modern medical information systems provide the necessary tools for the work of physicians in almost any specialty.