Four patients, aged 7–20 years, suffered from recurrent episodes of flaccid paralysis and encephalopathy associated with bilateral striatal necrosis and chronic progressive polyneuropathy. Using homozygosity mapping, a pathogenic missense mutation in the SLC25A19 gene that encodes the mitochondrial thiamine pyrophosphate transporter was identified. An SLC25A19 mutation was previously reported in Amish congenital lethal microcephaly but the present patients' phenotype is markedly different, with normal head circumference, normal early childhood development, age-appropriate cognitive skills, and normal urinary organic acid profile. Determination of the SLC25A19 sequence should be considered in patients with bilateral striatal necrosis and progressive polyneuropathy. Ann Neurol 2009;66:419–424