Background and Objectives: Posterior circulation ischemic stroke (PCIS) is a life-threatening disease with a poor prognosis. It has nonspecific symptoms. It is very difficult to diagnose. The aim of the study is to examine to what degree radiological methods, in addition to standard clinical indicators, can serve as a reliable and independent predictor of death in patients with PCIS. Materials and Methods: It is a retrospective study on 175 patients at the Special Hospital “Saint Sava” (2023–2025) with symptoms of acute PCIS, who did not have proven PCIS on the initial non-contrast computed tomography (NCCT). The radiology protocol included NCCT, CT perfusion (CTP) and CT angiography (CTA). The experimental group (n = 116, CTP+) and the control group (n = 59, CTP-) were monitored clinically and radiologically, with a follow-up NCCT after 24 h when all had confirmed acute PCIS. At discharge, the outcome was monitored on the National Institutes of Health Stroke Scale (NIHSS 2) and the Modified Rankin Scale (mRs). Results: Of 175 patients with acute PCIS, 24% died within 30 days. Those who died were older (p < 0.05), had a lower Posterior Circulation Alberta Stroke Program Early CT Score (pcASPECT), and more often had hyperdensity (26.2% vs. 7.5%), occlusions (69% vs. 31.6%), and symptomatic blood vessels on CTA and CTP+ (81% vs. 61.7%, p < 0.01). Multivariate regression singled out CTP+ (OR = 4.08), complications (OR = 2.96), Israeli Vertebrobasilar Stroke Scale (IVBSS) (OR = 1.22) and Trial of Org 10172 in Acute Stroke Treatment (TOAST) (OR = 1.92) as predictors of mortality, with shorter survival in CTP+ (949 vs. 1449 days, Log-rank p = 0.015), more NIHSS/mRS, lower Glasgow Coma Score, and more frequent obesity in the deceased. Conclusions: Negative CTP represents the protective factor against death in patients with acute PCIS. Complications, higher IVBSS, and TOAST classification (large vessels atherosclerosis) represent an increased risk. The importance of CTP for early detection of acute PCIS and early risk assessment is highlighted.