This chapter considers three groups, medically unexplained symptoms, somatoform disorders, and functional somatic syndromes. Describing the nature of these groups, it talks about their prevalence in cross-sectional studies in primary, secondary care and population-based studies. Medically unexplained symptoms are very common both in the general population and in primary and secondary care, but at least in the first two settings most are transient. Systematic reviews of the prevalence of irritable bowel syndrome in population-based samples have indicated that the prevalence varies considerably with the definition of the syndrome. Functional somatic syndromes are also common but only some patients with these syndromes also have numerous somatic symptoms. There is little doubt that somatoform disorders, or bodily distress syndromes, are an important and challenging group of conditions that are expensive in terms of healthcare use and time missed from work.