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Purpose/Objective(s): One of the most difficult steps of the radiotherapy is to determine the clinical target volume (CTV) based on the microscopic extension (ME). The aim of this study was to evaluate the ME in gliomas using consecutive macropathology. Another objective was to identify the predictive factors which could determine the ME. Materials/Methods: The study included glioma patients with tumor locating in the non-functional area and the gross maximal resection (between 2-3cm away from the tumor border) was performed. Tumor specimens were stained with hematoxylin and eosin (H&E) and immunohistochemistry of glial fibrillary acidic protein (GFAP) and S-100. Genetic status, including O(6)-methylguanine-DNA methyltransferase (MGMT), isocitrate dehydrogenase (IDH) and 1p/19q, were assessed. The ME from the center of the delineation of microscopic disease to the edge of primary tumor was measured. The correlation of these clinicopathological characters were evaluated by spearman's rank correlation. A predictive model was developed based on the coefficient of the spearman's rank correlation. Results: Totally, 552 slides obtained from 22 glioma patients were analyzed. The mean ME distance were 1.63AE0.53cm. High-grade glioma patients had significantly higher ME than low-grade glioma (1.85AE0.43cm vs. 1.12AE0.36cm, P < 0.001). A significant correlation was found between extent of ME and pathological grade (r Z 0.666, P < 0.001). Subventricular zone contact, cortical involvement, MGMT methylation, IDH wild and 1p/19q non-codeletion were also correlated with ME extent (r Z 0.359, 0.198, 0.313, 0.338, 0.200, respectively, all P < 0.01). Patients with invasive tumor cells far from the lesion (ME > 1.75cm) had worse prognoses than those in the neighboring only (17.4AE21.5months vs. 29.7AE16.8months; P Z 0.022). An invasive risk score model for predicting ME was developed: Y model Z 0.666X grade + 0.359X SVZ + 0.198X cortex + 0.313X MGMT + 0.338X IDH + 0.200X 1p/19q , the receiver operating characteristic curve (ROC) proved that the area under the curve of this model was 0.958 (95% confidence interval: 0.858-1.000, P Z 0.005). Conclusion: Glioma cells were heterogeneously distributed between the grades of patients. This suggested that the delineation of CTV should be individualized. The invasive risk score model could predict the ME of patients, and this may help the clinicians to determine the target volume of patients.