Medically unexplained symptoms are considered 'somatoform disorders' in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). The introduction of this nosographic category has been helpful in drawing attention to a previously neglected area, but has not been successful in promoting an understanding of the disorders' biological basis and treatment implications, probably because of a series of diagnostic shortcomings. The newly proposed DSM-V diagnostic criteria try to overcome the limitations of the DSM-IV definition, which was organised centrally around the concept of medically unexplained symptoms, by emphasising the extent to which a patient's thoughts, feelings and behaviours concerning their somatic symptoms are disproportionate or excessive. This change is supported by a growing body of evidence showing that psychological and behavioural features play a major role in causing patient disability and maintaining high level of health care use. Pain disorders is the sub-category of DSM-IV somatoform disorders that most closely resembles fibromyalgia. Regardless of the diagnostic changes recently brought about by DSM-V, neuroimaging studies have identified important components of the mental processes associated with a DSM- IV diagnosis of pain disorder.