Aims: This study aimed to unravel the dehydration status of patients with cerebral venous sinus thrombosis (CVST) to facilitate the understanding of dehydration in CVST. Methods: This was a multicenter retrospective study and three populations were recruited, namely, patients with CVST, CVST mimics, and healthy subjects. Blood samples were obtained 1-2 days after admission to assess dehydration status. Stata 15.1 was performed for statistical analysis. Results: A total of 208 patients were diagnosed with CVST, 237 with CVST mimics, and 200 healthy individuals were enrolled. The urine specific gravity (USG, 1.020 [1.014, 1.029] vs. 1.017 [1.011, 1.021]) was higher in patients with CVST than in those with mimics (all p < 0.001). The percentage of USG >1.03 was also higher in CVST (22.6%) than in its mimics (6.3%, p < 0.001). With the development of CVST, USG (acute vs. sub-acute vs. chronic, 1.022 [1.015, 1.033] vs. 1.021 [1.015, 1.031] vs. 1.019 [1.014, 1.025]) decreased. All dehydration-related markers could not differentiate CVST from its mimics and healthy populations, and they were not associated with CVST severity and prognosis (p > 0.05). Conclusion: High levels of USG, especially USG >1.013, were more common in patients with CVST. Dehydration-related indices could not characterize CVST and were not associated with CVST severity and prognosis.