Disclosed is the use of a pyrimidine nucleotide precursor selected from the group consisting of uridine, an acyl derivative of uridine, cytidine, and an acyl derivative of cytidine (wherein the preferred pyrimidine nucleotide precursor is 2',3',5'-tri-O-acetyluridine), for the manufacture of a medicament for treating or preventing a congenital mitochondrial disease selected from the group consisting of Mitochondrial Encephalomyopathy, Lactic Acidemia, Lerber's Hereditary Optic Neuropathy, Mitochondrial neurogastrointestinal encephalomyopathy, Progressive External Ophthalmoplegia, and Leigh's Disease, in a mammal.
