ObjectiveTo determine the time interval between symptom onset and neurologic deterioration related to cerebral edema in patients with massive middle cerebral artery infarction. The time period between onset and neurologic deterioration represents the window for surgical intervention.DesignMulticenter retrospective chart review.SettingsFive university-affiliated medical centers.PatientsFifty-three patients with massive middle cerebral artery infarction who experienced neurologic deterioration defined by a decrease in the Glasgow Coma Scale score of two or more points attributable to mass effect.Measurements and Main ResultsA total of 53 patients (mean age, 62 ± 18 yrs; 25 [47%] were men) with neurologic deterioration were identified by using International Classification of Diseases (9th revision) codes and local registries. Medical records and neuroimaging studies were reviewed by a stroke neurologist or neurointensivist to identify the time of neurologic deterioration. Thrombolytics were used at presentation in 19 (35%) patients. A total of 19 (36%) patients had neurologic deterioration within 24 hrs of symptom onset. By 48 hrs, 36 (68%) patients had manifested clinical deterioration. A few patients had later neurologic deterioration on day 3 (n = 10), day 4 (n = 2), day 5 (n = 2), and day 6 or after (n = 3). A total of 25 (47%) of the 53 patients died during hospitalization. The highest frequency of deaths occurred on day 3.ConclusionsNeurologic deteriorations related to cerebral edema after massive middle cerebral artery infarction occur in most patients within 48 hrs of symptom onset.