1H magnetic resonance spectroscopy (MRS) allows accurate and non-invasive in vivo metabolic study, and is a useful tool for the diagnosis of different forms of dementias. Cognitive impairment pathologies have been almost exclusively studied with MRS by comparison with healthy without a global comparison amongst Alzheimer disease (AD), vascular dementia, mild cognitive impairment (MCI) and major depression patients with cognitive impairment. Whereas decrease of N-acetylaspartate (NAA) and increase myo-Inositol (mI) at different brain locations by 1H MRS are common features of AD, Choline (Cho) alterations have been inconclusive. In our study, 64 patients with cognitive impairment were evaluated by 1H MRS using two echo times (31 and 136 ms). There were statistical differences between dementia (AD and vascular dementia) and non-dementia (MCI and depression) spectra at posterior cingulate gyrus. Cho/Cr, mI/Cr and NAA/Cr have been valuables for the differentiation amongst the different cognitive impairment entities. NAA/mI provides the best area under the ROC curve with the highest sensitivity (82.5%) and specificity (72.7%) in diagnosing AD. NAA/mI and mI/Cr ratios differed amongst the four cognitive impairment degenerative pathologies. Metabolic MRS differences found amongst patients with cognitive impairment entities can be useful to differentiate between AD, vascular dementia, MCI and depression.