Delayed cerebral ischemia remains a severe potential complication of aneurysmal subarachnoid hemorrhage (SAH) possibly leading to death and disability. We evaluated a semiquantitative and visual analysis of perfusion computed tomography (PCT) as a predictor of clinically relevant vasospasm (CRV) in patients with aneurysmal SAH. Thirty-eight patients with aneurysmal SAH were analyzed yielding 145 PCT scans. PCT, clinical examination, and transcranial Doppler ultrasound (TCD) were performed on days 3, 7, 10, and 14 after hemorrhage. Cerebral blood flow, cerebral blood volume, and time to peak (TTP) were analyzed semiquantitatively using six regions of interest, and visually for signs of cerebral hypoperfusion. CRV was defined as secondary cerebral infarction (CI) seen on cranial computed tomography scans and/or delayed neurological deterioration (DND). CI occurred in 13 (34.2 %) and DND in 11 patients (28.9 %). With TCD as pretest, TTP had a sensitivity of 90 % and a specificity of 72 % (cutoff value, 0.963) as predictor for CI. TTP's sensitivity as predictor for DND was 90 % with a specificity of 61.1 % (cutoff value, 0.983). Visual analysis of TTP showed a negative predictive value of 100 % with a positive predictive value of 52 %. TTP is a sensitive and specific perfusion parameter in predicting CI in patients with SAH. Its use in the clinical setting may optimize the early treatment of patients at risk for vasospasm before the onset of clinical deterioration, especially when applying TCD as pretest. Further investigation in a larger patient population is required.