There is an increasing interest in the use of the ketogenic diet (KD) as an adjuvant therapy for glioma patients. We assessed the tolerability and feasibility of a modified ketogenic diet (MKD) in patients with glioma, along with willingness of patients to participate in future randomized controlled trials. The study was undertaken in two parts; a patient questionnaire and evaluation of the diet. One hundred and seventy-two questionnaires were completed; 69% (n = 119) of the population reported MKD should be offered to patients with glioma and 73% (n = 125) would be willing to try MKD for 3 months. Six male patients with high grade gliomas tried the diet; 4 completed the 3-month feasibility period. Ketosis was achieved in all patients. The only gastrointestinal side effect was constipation (n = 2). Minimal changes were observed in weight, body mass index, fat mass and cholesterol profiles. MKD was well tolerated, with few side effects and is deliverable within a financially viable, NHS service. There is a high level of interest in the diet within the glioma patient community to ensure adequate recruitment for a clinical trial. Further studies are required to demonstrate efficacy and patient benefit before implementing a service.