Glioblastoma multiforme (GBM) is one of the most malignant CNS tumors. Despite advances in treatment modalities, it remains largely incurable. Several studies show that there is a promising survival advantage in treatment of GBM with extended temozolamide as compared to standard adjuvant six cycles. The aim is to evaluate the impact of extended 12 versus standard6 cycles of adjuvant temozolamide (TMZ) on overall survival and progression free survival in glioblastoma multiform patients. Patients and methods: The study was conducted on 40 newly diagnosed cases of glioblastoma referred to Zagazig University Hospital's Clinical Oncology and Nuclear Medicine Department, between January2018and January 2020.Eligible patients are adults between the age of18-65 years. They had normal liver and renal function tests, hemoglobin more than 10gm/dl and Karnofsky Performance Score (KPS) more than70. Patients with recurrent GBM or other active cancer or poor KPS were excluded. The patients were divided into 2 groups: group A included 20 patients treated by radiotherapy at a dose 60Gy/30fraction concurrently with TMZ for 6cycles (conventional TMZ) compared with group B which included 20 patients treated by the same concurrent chemo-radiotherapy regimen followed by 12 cycles of adjuvant TMZ (extended TMZ). RESULTS:The median progression free survival (PFS) was7.3 months and 5.6 months in extended TMZ and conventional TMZ respectively. Median overall survival (OS) was 12.4 months versus 10.8 in extended TMZ and conventional TMZ respectively. Conclusions: the study found that extended TMZ is well tolerated and is associated with increased PFS and OS in treatment of GBM, although being statically not significant. Further studies are needed to evaluate the extended treatment protocol