The major objective of the WHO International Study of Somatoform Disorders is an understanding of the somatic presentation of psychological problems in different cultures. Relying on an interdisciplinary approach which draws from anthropology and linguistics as well as psychiatry and epidemiology, the study has examined the cross-cultural applicability of symptoms and diagnostic criteria of somatoform disorders as defined in ICD and DSM. Moreover, it has developed a set of diagnostic instruments for the assessment of somatoform disorders in different cultures, including the Somatoform Disorders Schedule (SDS), the Somatoform Disorders Symptom Checklist, and the Screener for Somatoform Disorders (SSD). The study consists of two main phases. In the first phase, instruments for the assessment of somatoform disorders have been developed and tested for cross-cultural applicability, reliability and validity. In the second phase, using the instruments, the prevalence of somatoform disorders and their characteristics in different cultures are being assessed.