Fibromyalgia is a common but contested illness. Its definition and content have changed repeatedly in the 110 years of its existence. The most important change was the requirement for multiple tender points and extensive pain that arose in the 1980s, features that were not required previously. By 2010, a second shift occurred that excluded tender points, allowed less extensive pain, and placed reliance on patient-reported somatic symptoms and cognitive difficulties ('fibro fog') that had never been part of past definitions or content. Fibromyalgia is closely allied with and often indistinguishable from neurasthenia, a disorder of the late 19th and early 20th centuries that lost favour when it was perceived as being a psychological illness. Fibromyalgia's status as a 'real disease', rather than a psychocultural illness, is buttressed by social forces that include support from official criteria, patient and professional organizations, pharmaceutical companies, disability access, and the legal and academic communities.