Objective: To investigate the regional metabolite abnormalities and changes after treatment in patients with OCD with autogenous and reactive obsessions. Method: We assessed right anterior cingulate cortex (ACC) and amygdala-hippocampal region (Am+Hpp) N-acetyl-aspartate (NAA), choline (Cho) and creatine (Cr) concentrations and NAA/Cr and Cho/Cr ratios using single-voxel proton magnetic resonance spectroscopy in 15 patients with autogenous obsessions (OCD-A), 15 patients with reactive obsessions (OCD-R) and 15 healthy controls (HC). Measurements were repeated after 16weeks of fluoxetine treatment. Results: Baseline ACC NAA/Cr ratios of both OCD groups were significantly lower than HC. OCD-A group had significantly lower baseline NAA/Cr ratios in the Am+Hpp than other groups. These differences were more likely to be explained by higher Cr levels in ACC. We found no significant differences and changes for Cho levels and Cho/Cr ratios between groups and within groups. Significant increase in NAA/Cr ratios of OCD-A group found in the Am+Hpp was more likely to be explained by increased NAA levels. No significant changes were found in ACC NAA/Cr ratios. Conclusion: While disturbed energy metabolism in ACC might reflect a common pathology in patients with OCD regardless of symptom dimension, alterations in mesiotemporal lobe are more likely for autogenous obsessions. © 2011 John Wiley & Sons A/S.