Background: Somatoform disorders such as neurasthenia and chronic fatigue are characterized by a combination of prolonged fatigue and disabling neuropsychological and neuromuscular symptoms. However, the debate concerning the theoretical underpinnings of somatic disorders resembles the perennial dispute over the taxonomy of anxiety and depression. The objective of this study is to analyse the dimensional structure of items measuring anxiety, depression, phobic anxiety, somatic distress, and insomnia. It is anticipated that somatic distress should emerge as empirically distinct from measures of anxiety and depression, thereby lending support to proponents of the construct as independent of both anxiety and depression symptomatology. Methods: A 33-item self-report symptom inventory derived from the SCL-90 and DSSI/sAD scales was used to measure recently experienced psychiatric distress in the form of depression, anxiety, phobic anxiety, somatic distress, and insomnia. SCL and DSSI/sAD items were measured on a four-point distress scale from 1 'not-at-all' to 4 'unbearably'. The inventory was administered to a community-based sample of 3468 Australian twins between the ages of 18 and 28. Results: Factor analysis using Polychoric correlations and a Promax rotation criterion produced four factors: depression, phobic anxiety, somatic distress, and sleep disturbance. Conclusion: Results from the current factor analysis, together with the documented prevalence of somatic disorders, including evidence regarding the genetic and biological independence of somatic symptomatology, lend support to the argument that somatic symptoms, although correlated, are independent of anxiety and depression.