In 2007 a new clinical entity was described, anti-NMDA receptor (anti-NMDAR) encephalitis, an autoimmune, paraneoplastic disorder associated with IgG autoantibodies directed against NR1 subunit of the N-methyl-D-aspartate receptor. It is potentially lethal, but most often reversible form of encephalitis which responds to immunotherapy very well. This disease primarily affects young women and is often associated with ovarian teratoma. Epidemiological studies show that it is the most common form of autoimmune encephalitis, and it comes immediately after acute disseminated encephalomyelitis (ADEM). In 70% of patients the disease begins with a prodromal stage, and after 5-14 days the clinical picture is dominated by psychiatric symptoms, seizures, memory loss, decreased level of consciousness, and autonomic dysfunction often requiring mechanical ventilation. In order to make a diagnosis, the most important factor is the finding of specific antibodies to NMDA receptors in cerebrospinal fluid, along with lymphocytic pleocytosis. Therapy consists of the first (corticosteroids, therapeutic plasma exchange, intravenous immunoglobulins) and the second line of immunotherapy (cyclophosphamide, rituximab) along with the removal of tumor, if necessary. As no cases of anti-NMDAR encephalitis in the adult population in the Republic of Croatia have been described so far, the purpose of this study was to present six patients treated at the Department of Intensive Medicine and Neuroinfectology at the University Hospital for Infectious Diseases “Dr. Fran Mihaljević”, to whom this form of autoimmune encephalitis was proved. All patients were previously hospitalized at the psychiatric and/or neurological department and the average time which passed from disease onset to the diagnosis amounted to 32 days. The most prominent psychiatric symptoms were visual and/or auditory hallucinations as well as agitation, dominant sleep disorder was insomnia, and orofacial dyskinesia was the most common form of movement disorder. Tumor was found in only one patient, a right ovary teratoma. All patients responded positively to immunotherapy and relapse was not observed. Taking into account that 4-6% of patients with isolated psychiatric episodes have anti-NMDAR encephalitis, the primary purpose of this paper is to raise awareness among all clinicians, especially psychiatrists, neurologists and infectiologists, not only about a new clinical entity which deserves its place in differential diagnosis of acute and chronic psychosis, but also about the importance of seeking the organic cause in the apparently primary psychiatric disease.