Background and Purpose: Recurrent glioblastoma is a devastating disease with a poor prognosis. Our study delves into the outcomes of a significant number of patients diagnosed with recurrent glioblastoma and astrocytoma WHO grade 4, who underwent reirradiation with or without systemic therapy. The primary objective of our research was to examine the feasibility and associated toxicity of chemoradiation. In addition, we explored clinically relevant prognostic factors to help determine the most appropriate therapeutic approach for individual patients based on their prognosis. By shedding light on these critical factors, we hope to contribute to improving the outcomes and quality of life of patients with recurrent glioblastoma and astrocytoma WHO grade 4. Patients and Methods: Our retrospective observational study analyzed the data of 77 patients who had undergone reirradiation between January 2009 and June 2018. Reirradiation was carried out using conventional fractionated radiotherapy, either alone or in combination with systemic therapy. The median total radiation dose was 45 Gy (range: 18-62 Gy) administered in median fractions of 1.8 Gy per day (range: 1.8-18 Gy). Concomitant systemic therapy was administered to 60 patients (77.9%), and adjuvant sequential systemic therapy was given to 56 patients (72.7%). Results: Our study followed 77 patients who underwent reirradiation for recurrent glioblastoma and astrocytoma WHO grade 4, and after a median follow-up of 73.8 months, 87.0% (67/77) of patients had died. The median overall survival since reirradiation was 10.2 months (95%-CI, 8.0 – 12.3), with 1-year, 2-year, 3-year, and 5-year overall survival rates of 37.5%, 13.7%, 8.6%, and 3.4%, respectively. The median progression-free survival (PFS) according to RANO criteria was 5.8 months (95%-CI, 4.5 – 7.1), with 6-month PFS of 46.0% and 1-year, 2-year, 3-year, and 5-year PFS of 16.2%, 6.6%, 3.3%, and 1.7%, respectively. We found that the total contrast-enhancing tumor volume at the time of reirradiation was the most important predictor of overall survival (multivariate HR 1.042 per cm³, p < 0.001). A total volume of 20 cm³ was determined to be the optimal threshold for discriminating between patients with a favorable and unfavorable prognosis, based on maximum-rank statistics (p-value adjusted for multiple testing 0.004). Age was also an important predictor of overall survival after reirradiation (multivariate HR 1.034, p = 0.020), with the optimal age threshold for distinguishing good from poor performance patients determined to be 47 years using maximum-rank statistics (adjusted p-value = 0.056). Interestingly, we found that recurrence location outside of the primary treatment volume was the most important determinant of progression-free survival (multivariate HR 2.851, p = 0.002). However, we observed no significant difference in overall survival between patients with out-of-field and infield/marginal recurrences, respectively (univariate HR for OS 1.172, p = 0.603). Conclusion: Our findings suggest that conventional fractionated radiotherapy is a feasible and well-tolerated treatment option for glioblastoma recurrence. Moreover, our study demonstrates that the combination of chemoradiation can be a safe and efficient therapeutic modality. We also identified several clinically relevant prognostic factors that are important for making informed therapy decisions. Overall, our results provide important insights into the management of recurrent glioblastoma and highlight the need for personalized treatment approaches based on individual patient characteristics.