Background and Purpose: Cerebral venous sinus thrombosis (CVST) is one of the rare causes of cerebrovascular disease and has an extremely heterogeneous prognosis. The aim of this study was to investigate the potential relationship between early neurological deterioration, poor clinical outcome in CVST and the venous collateral score. Materials and Methods: A total of 121 patients diagnosed with CVST between 2010 and 2020 were retrospectively included. The demographic, clinical, and radiological findings related to venous sinus thrombosis and early neurological deterioration were investigated in relation to the clinical outcome. Results: The factors associated with early neurological deterioration were superior sagittal sinus thrombosis (P < 0.001), sinus rectus thrombosis (P = 0.031), parenchymal lesions (P < 0.001), and venous collateral score (P < 0.001). The factors associated with poor clinical outcome were superior sagittal sinus thrombosis (P < 0.001), cortical vein thrombosis (P < 0.001), venous collateral score (P < 0.001), and initial clinical symptoms. Binary logistic regression analyses revealed poor clinical outcome as a significant variable, with a venous collateral scale of 0 or 1 as a risk factor for a poor outcome (significance of the model P < 0.001). Conclusion: Early neurologic deterioration and poor clinical outcome may occur due to poor collateralization in CVST. Identifying the subgroup of CVST patients at risk of clinical deterioration is therefore important. This study highlights the clinical importance of venous collaterals; however, larger prospective multicenter studies are required to confirm the relationship with venous collaterals in patients with CVST.