OBJECTIVE:To characterize a scale for the measurement of fibromyalgia (FM)-like symptoms; to investigate whether FM is a discrete disorder; to understand the significance of FM-like symptoms; and to investigate causal and noncausal factors in the development of such symptoms. METHODS:We evaluated 25,417 patients with rheumatic disease using the Symptom Intensity (SI) Scale, a self-report scale that combines a count of pain in 19 nonarticular regions with a visual analog scale for fatigue. We studied this scale in relation to demographics, clinical symptoms, and serious outcomes, including serious medical illnesses, hospitalization, work disability, and death. RESULTS:Compared with other rheumatic disease assessments, the SI scale was the best identifier of symptoms associated with FM content, including an increase in general medical symptoms. SI scale elevations were associated with increases in cardiovascular disorders, hospitalization, work disability, and death. Persons with socioeconomic disadvantage by reason of sex, ethnicity, household income, marital status, smoking, and body mass had increased SI scores. For almost all clinical variables studied, the prevalence and/or severity of the variable increased linearly with SI scores. CONCLUSION:We identified a clinical marker for general symptom intensification that applies in all patients and is independent of a diagnosis of FM. We found no clinical basis by which FM may be identified as a separate entity. Higher scores on the SI scale were associated with more severe medical illness, greater mortality, and sociodemographic disadvantage, and these factors appear to play a role in the development of FM-like symptoms and symptom intensification.