The thalamus has been implicated in the pathophysiology of obsessive-compulsive disorder. Using a multislice spectroscopic imaging sequence, we reported reductions in right and left medial thalamic N-acetylaspartate/cytosolic choline + creatine/phosphocreatine and N-acetylaspartate/cytosolic choline levels in 11 pediatric patients with obsessive-compulsive disorder, 8 to 15 years, versus 11 case-matched healthy controls. These changes may reflect a change in N-acetylaspartate, cytosolic choline, or creatine concentrations. Therefore, using a validated phantom replacement methodology, we obtained absolute measures (mmol/L) of N-acetylaspartate, a putative marker of neuronal viability, cytosolic choline, and creatine in these subjects. A significant increase in cytosolic choline was observed in right and left medial but not lateral thalami in patients with obsessive-compulsive disorder versus controls. N-acetylaspartate and creatine did not differ significantly between case-control pairs in the medial or lateral thalamus. These findings provide new evidence of cytosolic choline abnormalities in the thalamus in pediatric obsessive-compulsive disorder.