Purpose Patients with glioblastoma are exposed to severe symptoms and organs failures (e.g., coma or acute respiratory failure), that may require intensive care unit (ICU) admission and invasive mechanical ventilation (IMV). However, only limited data are available concerning the prognosis of patients with glioblastoma receiving IMV. We sought to describe the reasons for ICU admission, and outcomes of patients with glioblastoma requiring IMV for unplanned critical complications. Methods In this retrospective analysis, four certified interdisciplinary brain tumor centers performed a retrospective review of their electronic data systems. All patients with glioblastoma admitted to an in-house ICU and receiving IMV between January 2015 and December 2019 were included. Clinical and prognostic factors as well as relevant outcome parameters were evaluated by group comparisons and Kaplan Meier survival curves. Results We identified 33 glioblastoma patients with a duration of IMV of 9.2 +/- 9.4 days. Main reasons for ICU admission were infection (n = 12; 34.3%) including 3 cases of Pneumocystis jirovecii pneumonia, status epilepticus (31.4%) and elevated intracranial pressure (22.9%). In-hospital mortality reached 60.6%. Younger age, low number of IMV days, better Karnofsky Performance Status Scale before admission and elevated intracranial pressure as cause of ICU admission were associated with positive prognostic outcome. Conclusion We conclude that less than 50% of patients with glioblastoma have a favorable short-term outcome when unplanned ICU treatment with IMV is required. Our data mandate a careful therapy guidance and frequent reassessment of goals during ICU stay.