Seven patients (mean age 7.7 yr) with Rett syndrome, a condition with progressive regression of psychomotor development are included in this study. Proton MR spectroscopy images were obtained with the multivoxel chemical-shift imaging mode TR 1500 ms; TE 40 ms: Spectra from 224 voxels in the brain parenchyma were studied. N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), and myoinositol (mI) peaks were quantitatively evaluated, and NAA/Cr, NAA/Cho, and Cho/Cr, mI/Cr ratios were calculated. Five age-matched normal cases were available as controls. In three patients with Rett syndrome spectroscopy ®ndings were normal, and the metabolite ratios were similar to control cases. In the remaining four patients with the syndrome prominent decrease of the NAA peak was the main ®nding resulting in decreases in NAA/Cr (1.14 ^17), and NAA/Cho (1.08 ^27) ratios p , 0:0001: Cho/Cr ratios (0.93 ^26), and mI/Cr ratios (0.88 ^36) were normal compared to controls. There was no correlation between spectroscopic changes and clinical status of the patients. The ®ndings suggested that not only reduced neuronal±dendritic arborizations but also decreased neuronal function could contribute to spectroscopy changes in Rett syndrome.