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To date, research in the field of genetics in psychiatric illness has yielded inconclusive results. The focus has primarily been on the nuclear genome, with relatively little attention paid to the mitochondrial genome. A growing body of evidence supports the hypothesis that mitochondrial dysfunction may be important in the biology of psychiatric disorders; therefore, we reviewed the literature on mitochondrial abnormalities and adult psychiatric disorders.We searched EMBASE, PsycINFO and MEDLINE (from inception - September 2011) and identified additional studies through review of reference lists of key articles.Patients with mitochondrial disorders display prominent psychiatric symptomatology, as seen by evidence from cross-sectional studies, case reports and case series. Mitochondrial DNA polymorphisms have been associated with several psychiatric illnesses including bipolar disorder, major depression, and schizophrenia, however, the literature demonstrates conflicting results and most studies have been underpowered. Despite some initial promising findings, the majority of studies have failed to find an association between mitochondrial DNA mutations and psychiatric illness. At the present time, there is not sufficient evidence to implicate any particular mitochondrial genetic variant in any disorder. Mitochondrial epigenetics, mitochondria-glucocorticoid interactions, disruption of neuronal oscillations and medication effects may all represent mechanisms by which mitochondria contribute to psychiatric illness.Patients with mitochondrial disorders can display prominent psychiatric symptoms and patients with psychiatric disorders may have an undiagnosed mitochondrial disorder. Additional studies incorporating larger samples are necessary to determine how mitochondrial genetics are involved in psychiatric illness to confirm these findings. Accumulating evidence also suggests involvement of mitochondrial dysfunction in the pathophysiology of psychiatric disorders, and therapeutic agents that target the mitochondria may be potentially effective treatments for psychiatric illness and merit further investigation.