To date, Streptococcus мassiliensis, the representative of human oral normobiota, was detected in the patients' blood only twice (which was confirmed by the reports published in 2004 and 2015). The patient with the demyelinating disease of the nervous system was routinely admitted to the neurological department for further examination and treatment. The diagnosis of meningoencephalitis was established based on the laboratory and instrumental tests. Meningoencephalitis was later complicated by bilateral multilobar pneumonia, systemic inflammatory response syndrome, and multisystem organ failure. After sharp deterioration of patient's health in the form of the decreased level of consciousness and brainstem symptoms, cerebrospinal fluid was tested by PCR for markers of viral and bacterial infections, and blood was cultured. Bacterial growth was detected in blood culture, and then Streptococcus massiliensis, susceptible to benzylpenicillin, vancomycin, levofloxacin, linezolid, sulfamethoxazole/trimethoprim, and erythromycin, was identified by time-of-flight mass spectrometry. Thus, it seems necessary to focus attention on this case of the Str. massiliensis isolation from blood due to the near total lack of data on the Str. мassiliensis biological role and the more frequent isolation of bacteria of the genus Streptococcus from sterile human body fluids.