OBJECTIVE: To investigate the characteristics of hydrogen proton magnetic resonance spectroscopy (H-MRS) in posterior portion cingulate gyrus and the correlations thereof with the results of mini-mental state examination (MMSE), Alzheimer disease assessment scale-cognitive (ADAS-cog) in patients with mild-moderate Alzheimer's disease (AD). METHODS: H-MRS in posterior portion cingulate gyrus was conducted in gender, age, and educational background-matched 24 patients with AD, 8 patients with vascular dementia (VD), and 11 normal controls (NC group) to measure the values of NAA (N-acetyl aspartate)myo-inositol (mI), and creatine and phosphocreatine (Cr). All the 4 subjects underwent MMSE and assessment with ADAS-cog as well. The correlations among these results were assessed. RESULTS: The NAA/Cr ratios in posterior portion cingulate gyrus of the AD and VD groups were (1.24 +/- 0.12) and (1.25 +/- 0.15) respectively, both significantly lower than that of the NC group [(1.46 +/- 0.19), P = 0.003, P = 0.017] without significant difference between the AD and VD groups (P = 0.800). The mI/Cr value of the AD group was (0.74 +/- 0.15), not significantly different from that of the VD group [(0.65 +/- 0.15), P = 0.153], and significantly higher than that of the NC group [(0.62 +/- 0.09), P = 0.007], however, the mI/Cr value of the VD group was not significantly different from that of the NC group (P = 0.662). If the NAA/Cr ratio < 1.31 was used as criteria of AD, the positive predictive value of AD was 73% and negative predictive value was 71%. The NAA/Cr ratio was positively correlated with the MMSE score (r = 0.731, P = 0.000), and negatively correlated with the ADAS-cog score (r = -0.541, P = 0.011). CONCLUSIONS: The NAA/Cr ratio decreases in the posterior portion cingulate gyrus of AD patients, and has statistical significant correlations with the score of MMSE and ADAS-cog. The H-MRS characteristics of posterior portion cingulate gyrus cannot effectively differentiate the early AD from early VD.