Introduction   The study of diseases determination methods is called «diagnostics» and is a main part of any medical speciality. Medical diagnostics is based on different methods of research and diseases determination, their severity and patient�s state of organism with the purpose to select and carry out necessary treatment and effective prophylactic measures, preventing the development of complications and recurring disease. Diagnostics is a complex cognitive process. Making out a diagnosis is connected with the whole number of problems: people are used to get tired and forget, they may also make careless mistakes or make hasty choice not taking into account an important symptom, which on the first sight may be feebly marked or does not exceed the value of the most vividly proceeding, but not the main symptoms. Purely classic manifestations of diseases occur seldom, more frequently there are various deflections or combinations of diseases, and as a result changes classic scheme of clinical course. It must be taken into consideration that dental and oral system, like other systems, usually responds by limited number of reactions on influence of different stimulants and etiological factors. It is also important to mention the fact, that similar in common features  of clinical presentation may be found at different in essence diseases. All described above is a very complex and hard systematic process, and this increases probability of error in the process. For this reason the dentist is not always able to gather necessary information coolly and religiously in order to make out precise and correct diagnosis�s, and this leads to undesirable and sometimes sad consequences as a result of wrong treatment. Here he may resort to an expert system, containing the knowledge, obtained at contact with the whole number of experts, working in this field, and information from reference-books and tutorials. In the form of such advising system stomatologist gets strong assistant and experienced colleague close at hand, with which he may consult in every difficult situation.   Research Topic Advising system diagnostics of stomatological diseases Research Methodology   Today, necessity of applying computer software in dentistry ( especially in diagnostics ) does not cause any doubt ( Special literature and statistical data processing improves it ). Our choice is Expert System using Artificial Intellect methods. Data ( knowledge ) basis created on the production ( rules ), frames and ( or ) ANN will definitely help dentists in exact diagnostics. The purpose of  given research is to understand algorithms of modern, current working systems and improve our choice of the way of programming. After realization of the best suitable algorithm in programming language the first aim is to fill base of knowledge with knowledge of skilled experts in dentistry. It�ll give us possibilities to correct working algorithms in process of introduction, by a principle of a feedback. Hypothesis Overall using of this system in dental clinics will help avoiding mistakes in diagnostics and will give a complete of the patient�s medical condition.  Research Results Introduction experience has showed, that as the time passes and the knowledge base grows, the system diagnoses more and more precisely. Advising system diagnostics of stomatological diseases doesn�t substitute dentist, but becomes irreplaceable assistant for him in practice.