Brain magnetic resonance spectroscopy in two patients with Leigh syndrome revealed the presence of lactate in gray and white matter brain tissue and relatively high choline levels in the white matter. The latter observation, most probably related to an ongoing demyelination process, underlines specific involvement of white matter metabolism in Leigh syndrome even in cases without involvement of the white matter as visualized on MRI. Magnetic resonance spectroscopy might thus be of help in differentiating Leigh syndrome from a range of other mitochondrial diseases, such as ophthalmoplegia and Kearns-Sayre syndrome, showing lack of lactate in brain tissues appearing normal on MRI.