AbstractAimsThis study aimed to unravel the dehydration status of patients with cerebral venous sinus thrombosis (CVST) to facilitate the understanding of dehydration in CVST.MethodsThis 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.ResultsA 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).ConclusionHigh 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.