There are no guidelines or prospective studies defining the optimal surgical treatment for gliomas of older patients (≥70 years) or those with limited functioning performance at presentation (KPS ≤70). Therefore, the decision between resection and biopsy is varied, amongst neurosurgeons internationally and at times even within an instiutition. This study aims to compare the effects of maximal tumor resection versus tissue biopsy on survival, functional, neurological, and quality of life outcomes in these patient subgroups. Furthermore, it evaluates which modality would maximize the potential to undergo adjuvant treatment. This study is an international, multicenter, prospective, 2-arm cohort study of observational nature. Consecutive HGG patients will be treated with resection or biopsy at a 3:1 ratio. Primary endpoints are: 1) overall survival (OS) and 2) proportion of patients that have received adjuvant treatment with chemotherapy and radiotherapy. Secondary endpoints are 1) proportion of patients with NIHSS (National Institute of Health Stroke Scale) deterioration at 6 weeks, 3 months and 6 months after surgery 2) progression-free survival (PFS); 3) quality of life at 6 weeks, 3 months and 6 months after surgery and 4) frequency and severity of Serious Adverse Events (SAEs). Total duration of the study is 5 years. Patient inclusion is 4 years, follow-up is 1 year.