Mitochondria are intracellular organelles crucial in the production of cellular energy. Mitochondrial diseases may result from malfunctions in this biochemical cascade. Several investigators have proposed that mitochondrial dysfunction is related to the pathophysiology of bipolar disorder (BD), major depressive disorder (MDD) and schizophrenia (SZ). The authors reviewed recent study findings and tried to delineate the current understanding of the correlation between mitochondrial dysfunction and psychiatric disorders. A growing body of evidence suggests that mitochondrial dysfunction is important in patients with psychiatric disorders. The evidence include impaired energy metabolism in the brain detected using results of magnetic resonance spectroscopy, electron microscopy, co-morbidity with mitochondrial diseases, the effects of psychotropics on mitochondria, increased mitochondrial DNA (mtDNA) deletion in the brain, and association with mtDNA mutations/polymorphisms or nuclear-encoded mitochondrial genes. It is possible that the new information will lead to a focus on psychiatric disorder as a metabolic disease. Treatment with psychotropics might ultimately enhance energy metabolism and reduce the damage of oxidative stress. The next step in the study of mitochondrial dysfunction in patients with psychiatric disorders should be clarification of how mitochondrial dysfunction, a nonspecific risk factor, causes specific symptoms. Further study of mitochondrial dysfunction in patients with psychiatric disorder is expected to be useful for the development of cellular disease markers and new psychotropics.