Purpose: The aim of the study was to examine the utility of PET with 11C-Methionine in diagnosis and evaluation of the treatment efficacy in childhood brain tumors.Methods: 16 PET-studies were performed in 11 children, 4-17years old, 3 boys and 8 girls, with brain tumors or tumor suspicion. Reasons for PET-study were an unclear diagnosis of tumor (7 cases), treatment efficacy definition (5 cases) and identification of tumor recurrence (3 cases). Studies were performed after i.v. injection of 11C-Methionine (6-9 MBq/kg). MRI or CT of brain was done before the PET-study in all patients. Diagnosis was confirmed by clinical follow-up or biopsy.Results: In 2 of 7 patients with suspicion of brain tumor no areas with pathological uptake of 11C-Methionine were found. In a patient with unclear tumor a benign process (ependimoma) was revealed that allowed avoiding a biopsy. A benign tumor detection in 2 patients with malignancy suspicion considerably affected treatment tactics. In 2 patients supposed benign growth was confirmed. In 2 of 3 patients with question of recurrence after surgery or radiotherapy and inconclusive MRI and CT picture malignant growth was found and in 1 patient was rejected. Repeated PET-studies in 2 patients with prolactinoma during therapy allowed prompt (within a few days) control of tumor response.Conclusion: The assessment of tumor metabolic activity in paediatric oncological practice using PET with 11C-Methionine is a reliable method in the correct indication of brain tumor origin and in prompt evaluation of treatment efficacy and control of recurrence.