Mitochondrial diseases are the most common group of inherited metabolic disorders with a collective incidence of 1.6:5.000, characterized by defects in oxidative phosphorylation and caused by mutations in genes in the nuclear DNA and mitochondrial DNA. Leigh syndrome is a rare neurodegenerative mitochondrial disease with an incidence of 1:40.000 live births. We report on a case of a 10 months old boy of gypsy origin, born at term in a no consanguineous healthy parents. The patient presented with hypotonia, convulsions, cutis laxa, dysmorphic features (cranium dolichocephalous, asymmetric face and ears), optic nerve atrophy, atrophy of distal leg muscles, hepatomegaly, episodes of opisthotonos position, frequent upper respiratory tract infections, frequent episodes of fever of unknown etiology, knee joint contractures. Blood lactate, amino acid and acylcarnitine profiles were normal. Magnetic resonance imaging (MRI) scans revealed symmetrical hyperintensity in T2-weighted images in white matter adjacent to the anterior and posterior horns of the lateral ventricles, hypogenesis of corpus callosum, atelectasis of left inferior pulmonary lobe. The results of the electromyography showed peripheric neuropathy, muscle hypotonia. The electroencephalography revealed epileptic activity. The electrocardiogram indicated irregular sinus rhythm, conduction disturbances in the Hiss fascicle on the right, right ventricular hypertrophy. Neurosonography was normal. The patient was initially suspected of having Krabbe disease but was not confirmed after genetic tests. Spinal muscular atrophy was also not confirmed by molecular genetics testing. The patient was evaluated and scored according to the Nijmegen Mitochondrial Disease Criteria Scale and accumulated a number of 8 points, which suggests the presence of a mitochondrial disease. Genetic analysis was performed using High Resolution Melting technique and the presence of point mutation m.3243A>G in the TL1 gene of the mitochondrial genome was identified. The diagnosis of Leigh syndrome should be considered in all cases involving children with neurological problems whenever symmetrical hyperintensity in T2weighted images are encountered on brain MRI.