PURPOSE: To demonstrate the proton MR spectroscopic characteristics of non-neoplastic focal basal ganglialesions with high signal intensity on long TR MR images in patients with neurofibromatosis type 1(NF-1), and tocompare them with those of normal-appearing basal ganglia in patients without focal lesions. MATERIALS AND METHODS: Single-voxel proton MR spectroscopy was performed in six patients with NF-1 from two families(three with andthree without non-neoplastic focal brain lesions). All six individual spectra were obtained from basal gangliawith voxel sizes of about 1 x 1 x 1 cm, three from focal pallidal lesions in patients with focal lesions and threefrom normal-appearing basal ganglia in patients without focal lesions. Spectra were acquired using a 1.5T clinicalMR imager and stimulated echo acquisition mode sequence, with the following parameters: 30 ms of echo time, 13.7ms of mixing time, and 2560 ms of repetition time. Zero and first-order phase correction was performed. RESULTS:N-acetyl aspartate(NAA)/creatine(Cr) ratios were similar between focal basal ganglia lesions and normal-appearingbasal ganglia, though the former showed slightly lower choline(Cho)/Cr ratios and slightly higher NAA/Cho ratiosthan the latter. Relatively enhanced resonances around 3.75 ppm, assigned as glutamate/glutamine, were observed inthe spectra of three focal lesions. Lipid resonances around slightly different positions were observed in all sixpatients, regardless of the presence or absence of focal lesions. CONCLUSION: Slightly decreased Cho levels andrelatively enhanced glutamate/glutamine resonances are thought to characterize the focal basal ganglia lesions ofNF-1. Different mobile lipids appear to be present in the basal ganglia of NF-1 patients, regardless of thepresence of focal lesions.