Mitochondrial encephalomyopathies encompass a group of disorders that have impaired oxidative metabolism in skeletal muscles and central nervous system. As the field of mitochondrial medicine takes shape and physicians in all specialties become increasingly aware of respiratory chain or oxidative phosphorylation (OXPHOS) related disorders, their prevalence remains largely unknown. The unique features of the mitochondrial genome and the dual control over this important cellular apparatus makes the clinical presentation variable and diagnosis difficult. There is a confounding variation in phenotype and genotype, and the natural history of the disorders in individual patients is not accurately predictable. Only recently have things begun to fall into place and some phenotypes defined. Diagnosis requires a complex battery of clinical studies coupled with diagnostic findings on muscle biopsy (abnormal structure, histochemistry, or enzyme studies) or DNA testing. However, a reasonably confident diagnosis can be made by viewing the clinical presentation in the light of family history and some basic, routinely available laboratory investigations. This review tries to give a brief account of mitochondrial structure, function and genetics, and clinical presentation, evaluation, and treatment in suspected cases of mitochondrial encephalomyopathies.