Although comorbid psychiatric illness is increasingly being recognized in patients with mitochondrial disorders, there has been relatively little attention to psychiatric symptomatology as the primary clinical presentation. The authors report detailed clinical, biochemical, neuroradiological, and genetic findings in a series of 12 patients with mitochondrial disorders in whom psychiatric symptoms were a prominent aspect of the clinical presentation. The psychiatric presentations included depression, anorexia nervosa, bipolar disorder, and obsessive-compulsive disorder. A review of the literature, in conjunction with the present series, indicates that psychiatric symptoms can be the presenting feature of mitochondrial disorders and highlights the importance of considering this diagnosis.