(Article in Lithuanian) - Despite improved understanding of the pathophysiology and the wider use of new molecular technologies for diagnosis, the etiological diagnosis of acute encephalitis remains undetermined in most cases. The incidence, prognosis, and severity of sequelae of this disease remain unknown. In France, according to published data, the incidence of encephalitis is estimated to be 1.9 cases per 100,000 inhabitants on average among non-HIV patients. The etiological diagnosis is established in less than 30% of cases. The most common diagnosis is herpetic encephalitis in adults and encephalitis caused by the varicella-zoster virus in children under 16 years of age. Despite the difficulty in diagnosis and the lack of specific treatment for most of these infections, the etiological diagnosis should always be thoroughly investigated to determine the individual prognosis, to allow for better management of antibiotic therapy, and to improve epidemiological knowledge. We present the recommendations established by the French Society for Infectious Diseases. Initially designed to reflect the French epidemiological context, they account for patients’ potential exposure to various epidemiological patterns. Three levels of etiological testing are proposed, ranging from the most common infections and those requiring immediate treatment to the rarest ones. (R.A.)