Delayed cerebral ischemia (DCI) is at presentation a diagnosis per exclusionem, and can only be confirmed with follow-up imaging. For treatment of DCI a diagnostic tool is needed. We performed a systematic review to evaluate the value of CT perfusion (CTP) in the prediction and diagnosis of DCI. We searched PubMed, Embase, and Cochrane databases to identify studies on the relationship between CTP and DCI. Eleven studies totaling 570 patients were included. On admission, cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and time-to-peak (TTP) did not differ between patients who did and did not develop DCI. In the DCI time-window (4 to 14 days after subarachnoid hemorrhage (SAH)), DCI was associated with a decreased CBF (pooled mean difference -11.9 mL/100 g per minute (95% confidence interval (CI): -15.2 to -8.6)) and an increased MTT (pooled mean difference 1.5 seconds (0.9-2.2)). Cerebral blood volume did not differ and TTP was rarely reported. Perfusion thresholds reported in studies were comparable, although the corresponding test characteristics were moderate and differed between studies. We conclude that CTP can be used in the diagnosis but not in the prediction of DCI. A need exists to standardize the method for measuring perfusion with CTP after SAH, and optimize and validate perfusion thresholds.