Autoimmune non-demyelinating diseases of the nervous system comprise a diverse and evolving group of rare disorders with varied pathophysiology, clinical presentation, and diagnostic criteria. This chapter reviews key syndromes including atopic myelitis, autoimmune encephalitis associated with antibodies against neuronal surface antigens, Bickerstaff’s brainstem encephalitis (BBE), chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids (CLIPPERS), Hashimoto encephalopathy, myasthenia gravis, and primary angiitis of the central nervous system (PACNS). Each disease is described with emphasis on epidemiology, immunological mechanisms, characteristic clinical syndromes, neuroimaging patterns, cerebrospinal fluid (CSF) findings, and available biomarkers. Particular focus is placed on distinguishing features that aid in differential diagnosis from demyelinating diseases such as multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). Diagnostic challenges, including antibody-negative presentations and antibody cross-reactivity, are discussed alongside evolving criteria and pitfalls. The chapter further addresses therapeutic approaches, including immunomodulatory and symptomatic treatments, and outlines prognostic considerations across the spectrum of these diseases. Early recognition and accurate diagnosis are critical to avoid misdiagnosis and delayed treatment, which can result in irreversible neurological damage. This chapter aims to provide neurologists and clinicians with a practical and updated reference to improve recognition, differentiation, and management of autoimmune non-demyelinating neurological diseases.