Background: Leigh syndrome (LS) is a rare and inherited disease which is associated with progressive neurological disorders. The molecular underlying mechanism in LS is defined with some defects in mitochondrial respiratory chain enzymes. Case presentation: Here, an 8-year-old girl is reported with bilateral horizontal gaze palsy, ataxia and drowsiness. She developed unsteady gait, drowsiness, progressive ataxia and intention tremor during her admission period. The laboratory tests were reported within normal values including biochemical, hematological, immunological, infectious and inflammatory markers and blood and cerebrospinal fluid (CSF) lactate. Brain magnetic resonance imaging (MRI) demonstrated dorsal midbrain, bilateral putamen nuclei and cerebellar dentate nucleus involvement. Ocular examination revealed retinal atrophy and pale disk in both sides. These symptoms were in favor of a neurodegenerative disorder. Magnetic resonance spectroscopy (MRS) revealed an elevated lactate peak in involved areas which suggested a mitochondrial disease. Finally, the molecular genetic test reported NDUFS4 gene mutation which confirmed the presence of Leigh syndrome. She responded significantly to mitochondrial treatment cocktail and clinical signs and symptoms improved gradually. NDFUS4 gene encodes a subunit of mitochondrial complex I (NADH: ubiquinone oxidoreductase) that removes electrons from NADH and transfers them to the electron acceptor ubiquinone. Conclusion: Our findings indicated that various symptoms and clinical features can be found in Leigh syndrome which could be probably due to different mutations in mitochondrial genes. Therefore, appropriate clinical and laboratory settings along with brain MRI, MRS and genetic test analysis would be necessary for the early diagnosis.