Glioblastoma is associated with a dismal prognosis with the standard of care involving surgery, radiation therapy and temozolomide chemotherapy. This review investigates the features that make glioblastoma difficult to treat and the results of glioblastoma immunotherapy clinical trials so far. There have been over a hundred clinical trials involving immunotherapy in glioblastoma. We report the survival-related outcomes of every Phase III glioblastoma immunotherapy trial with online published results we could find at the time of writing. To date, the DCVax-L vaccine is the only immunotherapy shown to have statistically significant increased median survival compared with standard-of-care in a Phase III trial: 19.3 months versus 16.5 months. However, this trial used an external control group to compare with the intervention which limits its quality of evidence. In conclusion, glioblastoma immunotherapy requires further investigation to determine its significance in improving disease survival.