Repeated apneic episodes during sleep may lead to cerebral damage in patients with obstructive sleep apnea (OSA). We performed proton magnetic resonance (MR) spectroscopic studies to examine cerebral metabolism in patients with OSA. We studied 15 healthy subjects and 23 patients with OSA who displayed no anatomical abnormalities on MR imaging. The patients were classified into two groups based on the results of polysomnography: mild OSA (11 patients) or moderate to severe OSA (12 patients). All the subjects were examined with two-dimensional chemical shift imaging. The N-acetylaspartate (NAA)/choline (Cho), NAA/creatine (Cre), and Cho/Cre ratios for cerebral cortex and white matter were calculated separately. A statistically significant intergroup difference was found for the NAA/Cho ratio in cerebral white matter (p < 0.005). This ratio was significantly lower in patients with moderate to severe OSA than in patients with mild OSA (p < 0.01) and healthy subjects (p < 0.01). Our findings indicate that cerebral metabolic changes occur in normal-appearing brain tissue in patients with moderate to severe OSA. The findings of a decreased NAA/Cho ratio suggests the presence of cerebral damage, probably caused by repeated apneic episodes. Proton MR spectroscopy may be useful for evaluating cerebral damage in patients with OSA.