A classic-MSUD patient was admitted at the age of 10 yrs because of severe neurological deterioration (ataxia, hallucinations, drowsiness) during severe decompensation due to gastroenteritis. Despite previous decompensation episodes, his neurological status was unremarkable. On admission, plasma leucine level was 1400 μmol/l, and BCAA-free aminoacid mixture (2 g/kg/ day) was immediately started. After 12 hours a brain MRI was performed, showing a picture resembling Wernicke encephalopathy (WE), characterized by FLAIR and DWI symmetric hyperintensity at the level of midbrain, hypothalamus, mamillary bodies and thalami. As WE is attributed to thiamine deficiency, thiamine supplementation (1 g/day i.v.) was started, with complete clinical and neuroradiologic recovery. A second classic-MSUD patient previously admitted with the same clinical picture and treated by analogous dietary adjustments, was retrospectively recognized with WE-like MRI lesions. The patient recovered completely even without thiamine supplementation. As WE pathophysiology seems to be mainly due to α-ketoglutarate dehydrogenase (α-KGDH) inhibition, we hypothesized a possible common pathogenesis of neuronal damage between the two disorders. Interestingly, α-ketoisocaproic acid was shown to selectively inhibit α-KGDH in brain mitochondrial preparations (Amaral AU, 2010) . These findings might explain the neuroradiological picture of WE in MSUD and its reversibility with decompensation treatment, furthermore MSUD should be included as a cause of WE. Background: Tyrosinaemia type III (4-hydroxyphenylpyruvate dioxygenase deficiency) is extremely rare and the cognitive outcome is not well defined.