The present invention relates to the use of individual fumaric acid derivatives or mixtures thereof for preparing a pharmaceutical composition for treating mitochondrial diseases, especially for treating Parkinsons syndrome, Alzheimers disease, Chorea Huntington disease, retinopathia pigmentosa and mitochondrial encephalomyopathy. Preferably, the fumaric acid derivative(s) is/are those selected from the group consisting of fumaric acid dialkyl esters or fumaric acid monoalkyl esters in the form of the free acid or a salt thereof.
