Patients with neuromyelitis optica (NMO) often have an accompanying autoimmune disease, most commonly, but not limited to Sjögren's syndrome (SS). The aim of this study was to compare clinical and laboratory features between NMO patients with and without SS and to investigate the prognosis of NMO in patients with and without SS. Twenty-three NMO patients with SS and 42 NMO patients without SS were included. Clinical and laboratory profiles were compared, including annual relapse rate and time from onset of NMO to Expanded Disability Status Scale (EDSS) scores of 4.0 and 6.0. More NMO patients with SS than those without SS had anti-nuclear antibody, anti-SS-A/Ro and anti-SS-B/La antibodies (91.3 vs. 35.7%, p < 0.001, 87.0 vs. 2.3%, p < 0.001, and 34.8 vs. 0.0%, p < 0.001, respectively). Serum immunoglobulins (IgA, IgM and IgG) were markedly increased in NMO patients with SS in comparison with those without SS. Annual relapse rate and the time from disease onset to an EDSS score of 4.0 and 6.0 were not significantly different between the two groups. No differences between the two groups were found for the other parameters, including AQP-4 antibody status, length of spinal cord lesion and brain lesions. These results imply that NMO in SS more likely represents coexistence with SS rather than representing the result of direct central nervous system involvement in SS. Autoimmune response appears to be more intense in the NMO group with SS, but did not cause a more severe prognosis in comparison with the group without SS, indicating that we should pay attention to the potential benefit of the antinuclear antibodies in NMO.