BACKGROUND: Risk factors and mechanisms of cognitive impairment (CI) after aneurysmal subarachnoid hemorrhage (aSAH) are unclear. This study used a neuropsychological battery, MRI, ERP and CSF and plasma biomarkers to predict long-term cognitive impairment after aSAH. MATERIALS AND METHODS: 214 patients hospitalized with aSAH (n = 125) or unruptured intracranial aneurysms (UIA) (n = 89) were included in this prospective cohort study. Neuropsychological tests were administered 7 to 24 months post-discharge. MRI, ERP, and CSF and plasma biomarkers were used to predict long-term CI, and area under ROC curves were calculated. RESULTS: Patients with aSAH CI showed significant impairment across composite scores and cognitive domains on the neuropsychological battery vs. patients with aSAH No CI. On ALFF (MRI), the right medial orbitofrontal cortex (AUC = 0.78), right inferior frontal gyrus (AUC = 0.848), and right inferior parietal lobule (AUC = 0.868) distinguished aSAH CI from aSAH No CI. For ERP, consistent changes were found across specific EEG electrodes (FP1, F3, CP1, FP2, F4, CP2), including increased PA, prolonged PL and decreased ITPC. ITPC showed the highest sensitivity for distinguishing aSAH CI from aSAH No CI, followed by PA. Channel F4 (ITPC, AUC = 0.912, PA, AUC = 0.846), corresponding to the right inferior frontal gyrus, was the most sensitive for detecting CI, followed by channel CP2 (ITPC, AUC = 0.903, PA, AUC = 0.806), corresponding to the right inferior parietal lobule. CSF (Aβ42, Aβ40, p-tau181/Aβ42, p-tau181/total-tau, total-tau) and plasma biomarkers (Aβ-40, p-tau181) were significantly associated with long-term CI. CONCLUSION: ALFF, ERP, and CSF and plasma Aβ and tau levels and ratios have clinical utility for evaluating and predicting long-term cognitive impairment following aSAH. MRI may reveal the pathogenesis of cognitive impairment following aSAH. ERP can be administered at the bedside offering sensitive, non-invasive, repeatable, and sustainable monitoring, which is particularly suitable for immobile coma patients. ERP may represent a promising method to monitor neural function and its outcomes.