This is an unblinded, open labelled stratified randomised Phase II multicentre clinical trial (CTIMP). 120 patients with newly diagnosed de-novo glioblastoma following surgery or biopsy and radical radiotherapy with concomitant temozolomide will be recruited from 7 sites in the UK. Patients who meet the eligibility criteria will be randomly allocated to receive either ipilimumab and temozolomide or temozolomide alone.