Uptake of the neurotransmitter glutamate is effected primarily by transporters expressed on astrocytes, and downregulation of these transporters leads to seizures and neuronal death. Neurons also express a glutamate transporter, termed excitatory amino acid carrier–1 (EAAC1), but the physiological function of this transporter remains uncertain. Here we report that genetically EAAC1-null (Slc1a1^−/−) mice have reduced neuronal glutathione levels and, with aging, develop brain atrophy and behavioral changes. EAAC1 can also rapidly transport cysteine, an obligate precursor for neuronal glutathione synthesis. Neurons in the hippocampal slices of EAAC1^−/− mice were found to have reduced glutathione content, increased oxidant levels and increased susceptibility to oxidant injury. These changes were reversed by treating the EAAC1^−/− mice with N-acetylcysteine, a membrane-permeable cysteine precursor. These findings suggest that EAAC1 is the primary route for neuronal cysteine uptake and that EAAC1 deficiency thereby leads to impaired neuronal glutathione metabolism, oxidative stress and age-dependent neurodegeneration.