Introduction: Mitochondrial encephalopathy is a rare genetic disease with a varied symptomatology and represents a major diagnostic problem.Aim: Monitoring of the clinical- paraclinical manifestations in order to confirm the diagnosis of mitochondrial encephalopathy. Materials and methods: There were investigated seven children between 3-15-year-old suspected by a positive diagnosis of mitochondrial encephalopathy. The following laboratory tests were performed: serum creatinine, creatinine kinase, serum lactate, EMG, brain CT, brain MRI, muscle biopsy. Results: We observed that children suspected with mitochondrial encephalopathy often presented in neurological manifestations: neuropsychological retardation, myoclonic epilepsy, headache, pseudoictale seizures, vomiting, ataxia, sensory hearing loss, dementia, retinitis pigmentosa; and extraneurological: hypertrophic cardiopathy, endocrine disorders, iron-deficiency anemia, lactic acidosis, physical retardation, short stature. Laboratory tests revealed lactic acidosis in six cases and hyperpyruvatemia in one case. Muscular biopsy: in five cases- presence of red muscle fibers in flaps. EMG pattern: in four casesmyopathic potential, in three cases - signs of peripheral neuropathy. MRI scan: in three cases - hypodense foci, in two cases - cortical atrophy, in one patient- hyperintense areas were found in the basal ganglia and brainstem, in another case - calcification in the basal ganglia. The study was mainly based on characteristic clinical signs, MRI pattern and muscle biopsy. Conclusions: We suggest that the heterogeneous symptomatology of mitochondrial encephalopathy is one of the causes why patient see different specialists in order to seek the diagnosis. The most common clinical symptoms are brain, muscle, cardiac and neuro. The suggestive symptoms of CNS damage are the most frequent in these patients. The genetic test and neuroimaging method have the major role in mitochondrial encephalopathy diagnosis confirmation. The presence of red fibers in skeletal muscle and the biochemical results characteristic to the mitochondrial defects support the diagnosis. But, the decisive diagnostic test represents the DNAmt molecular analysis.