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Background: Autoimmune encephalitis (AIE) and paraneoplastic syndromes (PNS) are both rare groups of neurological diseases that are difficult to diagnose., Aim: We aimed to determine the common and distinct aspects of these two aetiologies of encephalitis as well as the characteristics of our patient group., Methods: We respectively analysed the records of the patients including symptoms, demographic features, neurological examination, cranial-magnetic-resonance-imaging (MRI), electroencephalography (EEG) findings, cerebrospinal fluid results (CSF) findings. Autoimmune/paraneoplastic autoantibodies in blood and/or CSF were all documented., Results: Forty-six patients fulfilled the diagnostic criteria. Thirty-eight of them were diagnosed with AIE, and 8 of them were diagnosed with PNS. The PNS group had higher nonconvulsive status epilepticus than the AIE (2/8 vs 0/38; p=0.027). PNS patients were diagnosed with a malignancy in their follow-ups more than those in the AIE group [4/38 vs 8/8] (p<0.001). When the symptoms of antibody-positive and negative patients were compared in the AIE group, the rates of consciousness/memory problems (13/15 vs 11/23; p=0.020) and speech impairment (8/15 vs 2/23; p=0.004) were significantly higher in patients without antibodies (n: 15) than in antibody-positive patients (n: 23). In antibody-negative groups, the rates of memory problems in neurological examination (13/15 vs 12/23 p=0.028) and temporal findings on electroencephalography were more prominent than antibody-positive groups (1/23 vs 5/15; p=0.027). The number of patients with cerebellar signs was higher in antibody-positive patients (6/23 vs 0/15; p=0.038)., Conclusion: Although the positivity of autoantibodies is critical in the diagnosis of AIE and PNS, even minor differences in clinical and laboratory findings of patients are helpful in the diagnosis, especially in the autoantibody-negative patients. Comparing the data with other population studies has shown that several inherited and environmental factors may contribute to the pathophysiology of AIE and PNS, as well as clinical and laboratory differences., (© 2022. Fondazione Società Italiana di Neurologia.)