<p>Previous studies have proposed the modified World Federation of Neurosurgical Societies (m-WFNS) scale, which assesses impaired consciousness without considering neurological symptoms, as a simpler and more reliable predictor of outcomes before aneurysmal subarachnoid hemorrhage (aSAH) treatment. However, large-scale external validation of the m-WFNS scale is lacking. This study aimed to perform an external validation of the m-WFNS scale and identify suitable subgroups using data from a prospective nationwide hospital-based registry from 2000 to 2020. We included 6,607 patients with single ruptured saccular aneurysms treated within 72&#xa0;h of onset. The original WFNS (o-WFNS) grades II and III were reclassified as m-WFNS grades II for the Glasgow Coma Scale 14 and III for the Glasgow Coma Scale 13. The predictive accuracies for unfavorable outcomes, defined as modified Rankin Scale 3 or higher at discharge, were compared. The areas under the receiver operating characteristic curve for the o-WFNS and m-WFNS were 0.781 and 0.783, respectively (p-value, 0.01), demonstrating better calibration of the m-WFNS scale. Subgroup analysis showed significant improvements in predictive accuracy for patients younger than 75 years, Fisher group 3 subarachnoid hemorrhage, an aneurysm size of 6–14&#xa0;mm, anterior communicating artery aneurysms, and internal carotid artery-posterior communicating artery aneurysms. No difference was observed for middle cerebral artery aneurysms. The m-WFNS, a simplified consciousness-based scale, demonstrated better predictive accuracy, particularly for anterior communicating artery and internal carotid artery-posterior communicating artery aneurysms. This scale will allow clinicians to easily predict prognostic prospects before treatment initiation.</p>