Subacute necrotising encephalopathy or Leigh syndrome is a congenital neuro-metabolic disease that is part of a group of diseases called mitochondrial encephalopathies. The form inherited is variable and it has a multisystemic effect, although with a predominance of lesions in the central nervous system. Prognosis is poor and there is no specific treatment for it. In 2007, we published the case of a 23-year- old patient, with severe psychomotor agitation crises, who responded favourably to lithium1 after the failure of several previous treatments. Here, we describe the follow-up of this patient during the 5 years after discharge from hospital, until her death at 29 years of age. Her improvement was maintained, she was not hospitalised again and the patient’s level of autonomy increased. The possible relationship of this improvement to new data on the neuroprotective and neurotropic effects of lithium are discussed.