In recent years, there has been growing interest in the human gut microbiota, whose health is characterised by high microbial diversity. Through the gut-brain axis, the microbiota influences the homeostasis of the central nervous system by regulating neurological, immune and epigenetic functions. Intestinal dysbiosis is associated with various neurological and oncological diseases, including paediatric diseases and colorectal cancer. Recent studies highlight a significant link between microbiota and brain tumours: cancer patients show reduced microbial richness and altered bacterial composition. In addition, an intratumoural microbial population has been identified that can influence tumour initiation, progression and response to therapies by modulating tumour cells and the immune system. The aim of this study is to analyse stool samples to study the microbiota in children suspected CNS brain tumor as there are currently no studies of this kind reported in the literature to assess whether microbial changes can be detected at diagnosis, can be found during the course of the disease or are associated with tumour progression.