Backgrounds　and　Objectives:　Patients　with　thyroid　dysfunction　frequently　have　neuropsychiatric　complaints　such　as　lack　of　concentration,　poor　memory,　depression,　anxiety　and　mania,　which　suggest　brain　dysfunction.　However,　the　underlying　process　of　this　dysfunction　remains　unclear.　Recent　studies　of　the　glutamatergic　system　have　offered　important　insight　into　the　neuropsychiatric　process.　Thus,　this　study　investigates　changes　in　glutamate　concentration　in　patients　with　thyroid　dysfunction.　It　also　clarifies　whether　Glu　levels　are　related　to　thyroid　hormones　via　proton　magnetic　resonance　spectroscopy.　Methods:　36　untreated　patients　with　thyroid　dysfunction　(18　hyperthyroidism　patients　and　18　hypothyroidism　patients)　and　18　age-　and　gender-matched　controls　were　included　in　this　study.　The　posterior　cingulate　cortex　was　examined　by　MRS　with　TB-averaged　PRESS　at　3　T.　The　intensity　of　glutamate,　choline,　N-acetylaspartate,　and　creatine　was　assessed　using　jMRUI　v4.0　software.　Results:　We　found　a　significant　difference　among　hyper-/hypo-　and　control　groups　in　Glu　(P　=　0.003)　and　Cho　(P　=　0.015).　The　concentrations　of　glutamate　increased　(P　=　0.006)　in　the　posterior　cingulate　cortex　in　patients　with　hypothyroidism　and　significantly　decreased　(P　=　0.002)　in　hyperthyroidism　patients　relative　to　controls.　There　were　no　difference　in　the　concentrations　of　choline　between　hyperthyroidism　patients　and　controls　(P　=　0.679).　Versus　the　hyperthyroidism　group,　the　hypothyroidism　group　showed　increased　glutamate　(P　=　0.018)　and　choline　(P　=　0.001)　in　the　posterior　cingulate　cortex.　There　was　no　significant　difference　in　the　concentrations　of　NAA　or　creatine　across　the　three　groups　(P＞　0.05).　The　Glu　level　correlates　with　173　(P　=　0.000)　and　FT3　(P　=　0.022).　Conclusion:　The　signal　intensity　of　glutamate　shows　significant　differences　in　the　region　of　the　posterior　cingulate　cortex　in　patients　with　thyroid　dysfunction.　This　change　indicates　a　potential　role　of　glutamate　in　the　brain　dysfunction　experience　by　patients　with　thyroid　hormone　disorders.　(C)　2015　Elsevier　Inc.　All　rights　reserved.