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 ins, 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 findings 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 finding 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 findings suggested that not only reduced neuronal-dendritic arborizations but also decreased neuronal function could contribute to spectroscopy changes in Rett syndrome. (C) 2002 Elsevier Science Ltd. All rights reserved.