Multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) are inflammatory diseases of the central nervous system and inflammatory conditions involving sleep-related anatomical structures, associated with sleep-related disorders. After the identification of pathogenic anti-aquaporin-4 antibodies, NMOSD–previously considered a variant of MS–is now regarded as a distinct entity. A higher prevalence of sleep-related disorders is reported in individuals with MS compared to the general population, and recent evidence suggests the same is true in NMOSD. Timely recognition and multidisciplinary therapeutic approaches for sleep-related disorders in individuals with MS or NMOSD improve the patient’s quality of sleep and life. Therefore, this review aims to provide clinicians with a comprehensive understanding of the comorbid conditions and diagnostic and therapeutic strategies in clinical practice.