Background: Glioblastoma Multiforme (GBM) is the most common primary intracranial tumour of the brain. The standard of care first line management is maximum safe debulking followed by concurrent chemo radiation (Stupp et al, 2005). In spite of further recent advances, median survival still remains poor and ranges between 14 to 21 months, especially in the MGMT unmethylated group. There are no randomised trials investigating less than 6 cycles of adjuvant temozolomide (TMZ). In our study we retrospectively analyse the impact on overall survival (OS) and progression free survival (PFS) in cases where adjuvant treatment has been discontinued due to toxicity or patient’s fitness Methods: We collected data from 2007 to 2016 for a cohort of patients who underwent adjuvant treatment for GBM following histological diagnosis. The final analyses included patient’s who completed concurrent chemoradiotherapy to a dose of 60 Gray in 30 fractions and had at least one cycle of adjuvant TMZ chemotherapy Results: Of 110 patient cohorts, 57% of patients completed adjuvant chemo radiotherapy followed by 4-6 cycles of adjuvant TMZ, 43% received 3 or less cycles of TMZ. Overall PFS was 11.9 months. Those that completed 4 or more cycles of adjuvant TMZ had an improved PFS (Log rank test P-value 0.001) versus those that completed 3 or less cycles. On cox analysis the number of adjuvant cycles of TMZ significantly affects OS, P-value 0.0003. Median overall survival was 16 months for the whole group, but was 10 vs. 20 months for the two groups. On cox analysis we also identified second line chemotherapy had a significant impact on OS (cox model P-value 0.002) Conclusions: We identified patients receiving three or fewer cycles of adjuvant TMZ had poorer outcomes. Second-line chemotherapy improved outcomes at relapse regardless of redo surgery.