We describe a case of a brainstem glioma (BSG) occurred in an adult patient with neurofibromatosis type 1 (NF1) and evaluated by Flourine-18-Fluorodeoxyglucose-positron emission tomography/computed tomography (18F-FDG-PET/CT). A 32-year-old male patient with NF1 underwent brain magnetic resonance imaging (MRI) for the onset of diplopia, facial paresis and cerebellar signs and symptoms. MRI showed a brainstem lesion compatible with BSG. Biopsy was not performed. 18F-FDG-PET/CT demonstrated intense 18F-FDG uptake in the brainstem lesion, suggesting an aggressive neoplasm. The patient was referred to radiotherapy but he developed rapid disease progression. In this case, 18F-FDG-PET/CT provided useful information about this rare NF1-associated tumor (Figs. 1 and 2).