90 Background: To date it is unclear when patients with high grade glioma (HGG) lose their capacity to make decisions during the end-of-life (EoL) phase. EoL symptoms have not been prospectively assessed. The goal of this prospective single center study was to assess the symptom burden in terminal HGG patients with a special focus on symptoms related to decision making capacity during the last 3 months of life. Methods: Patients with HGG, failing 3rd line therapy, showing clinical and/or radiological progression with a Karnofsky Performance Status score < 60 were eligible for enrollment. A baseline MD Anderson Symptom Inventory Brain Tumor Module (MDASI-BT) was performed upon enrollment. Patients or surrogates received bi-weekly telephone calls to repeat the MDASI-BT. Calls continued until death, or refusal to participate. Symptoms were stratified by weeks prior to death. Mixed models were used to assess for symptom and interference changes over time. Overall time effect was tested at the 0.05 level. If significant, pairwise comparisons of the time groups were done. Testing level was set at 0.01 to take into account the large number of comparisons. Results: Symptom scores of 52 patients are available for analysis. Symptoms involved in decision making such as speaking, concentrating, drowsiness (all p < 0.001), and understanding (p < 0.011) started to decline severely 12 weeks prior to death. The cognitive construct (understanding, remembering, speaking, concentrating) was significantly impaired during the last 2 weeks of life and started to deteriorate after week 12 (p < 0.001). The decision making composite score (understanding, speaking, concentrating, fatigue, drowsiness) showed the same pattern (p < 0.001). Overall disease burden also significantly increases within the last 2 weeks of death. Conclusions: Patients with HGG have a high symptom burden during the active EoL phase, increasing significantly during the last 12 weeks prior to death. Symptoms interfering with decision making capacity increase after week 12 and reach their peak 2 weeks prior to death. These findings stress the importance of early initiation of palliative care and advance care planning in patients with HGG.