In vivo nuclear magnetic resonance spectroscopy (MRS) has been developed recently in order to analyze brain metabolism in adults and children. After a short presentation of the methods and of the metabolic signals detected by phosphorus and proton MRS of the brain, the impact of MRS in pediatrics is examined with two main indications: the study of cerebral maturation in normal or pathological neonates, and the study of inborn metabolic encephalopathies. In the near future, brain MRS will be performed routinely after conventional MRI, and will become a valuable metabolic complement to the anatomical evaluation of cerebral pathologies.