Background: Secondary neurological deterioration in patients with spontaneous intracerebral hemorrhage (sICH) develops within the first 24 or 48 h after ICH onset and appears to portend a poor prognosis. We aimed to verify whether hypodensities within an acute ICH detected by noncontrast computed tomography (NCCT) were able to predict secondary neurological deterioration and investigate which monitoring window was of the highest predictive value. Materials/methods: This study involved sICH patients from three clinical centers of Fudan University between October 1, 2016 and March 31, 2018. Logistic regression analysis was used to assess the association between hypodensities and secondary neurological deterioration. The receiver operating characteristic curve of the subjects was performed to evaluate the critical value of the detection time window of hypodensities that best predicted the secondary neurological injury. Then, we divided the detection time window of hypodensities into 0-1.5 h, 1.5-3 h, 3-4.5 h and 4.5-6 h, and calculated the sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV) and accuracy respectively. Results: A total of 240 ICH patients met the inclusion criteria, 97 (40.42%) of whom were observed secondary neurological deterioration. Hypodensities were positive in 113 patients (47.08%), and more common in patients with secondary neurological deterioration (76.25%). The multivariate logistic regression analysis demonstrated that infratentorial hemorrhage (P < .001), the baseline hematoma volume (P = .015), and the presence of hypodensities on admission CT scan (P < .001) were independent predictors of secondary neurological deterioration. The sensitivity, specificity, PPV, and NPV of hypodensities in predicting secondary neurological deterioration were 76.3%, 72.7%, 65.5%, and 81.9%, respectively. When the time to the baseline NCCT was 114.5 min, the hypodensities were of the highest predictive value. Besides, the risk of secondary neurological deterioration predicted by hypodensities detected during 1.5-3.0 h was higher than other time periods. Conclusions: Hypodensities within hematoma detected by an NCCT scan may predict secondary neurological deterioration, independent of other clinical and imaging predictors. Hypodensities detected at 1.5-3.0 h after ICH onset have better predictive efficacy.