Thomas Meinertz Dantoft,1 Jeanette Frost Ebstrup,1 Allan Linneberg,1–3 Sine Skovbjerg,1 Anja Lykke Madsen,1 Jesper Mehlsen,4 Louise Brinth,4 Lene Falgaard Eplov,5 Tina Wisbech Carstensen,6,7 Andreas Schroder,6,7 PerKlausen Fink,6,7 Erik Lykke Mortensen,8 Torben Hansen,9 Oluf Pedersen,9 TorbenJørgensen1,10,11 1Research Centre for Prevention and Health, The Capital Region of Denmark, Glostrup, 2Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, 3Department of Clinical Experimental Research, Rigshospitalet, Glostrup, 4Coordinating Research Centre, Bispebjerg and Frederiksberg Hospital, Frederiksberg, 5Mental Health Centre Copenhagen, Research Unit, Mental Health Services, Capital Region of Denmark, Copenhagen, 6The Research Clinic for Functional Disorders and Psychosomatics, Aarhus University Hospital, 7Faculty of Health Sciences, University of Aarhus, Aarhus, 8Department of Public Health and Center for Healthy Aging, 9NovoNordisk Foundation Center for Basic Metabolic Research, 10Department of Public Health, Faculty of Health and Medical Sciences, University of Copenhagen, 11Faculty ofMedicine, Aalborg University, Aalborg,Denmark Abstract: The Danish study of Functional Disorders (DanFunD) cohort was initiated to outline the epidemiology of functional somatic syndromes (FSS) and is the first larger coordinated epidemiological study focusing exclusively on FSS. FSS are prevalent in all medical settings and can be defined as syndromes that, after appropriate medical assessment, cannot be explained in terms of a conventional medical or surgical disease. FSS are frequent and the clinical importance varies from vague symptoms to extreme disability. No well-described medical explanations exist for FSS, and how to delimit FSS remains a controversial topic. The specific aims with the cohort were to test delimitations of FSS, estimate prevalence and incidence rates, identify risk factors, delimitate the pathogenic pathways, and explore the consequences of FSS. The study population comprises a random sample of 9,656 men and women aged 18–76years from the general population examined from 2011 to 2015. The survey comprises screening questionnaires for five types of FSS, ie, fibromyalgia, whiplash-associated disorder, multiple chemical sensitivity, irritable bowel syndrome, and chronic fatigue syndrome, and for the unifying diagnostic category of bodily distress syndrome. Additional data included a telephone-based diagnostic interview assessment for FSS, questionnaires on physical and mental health, personality traits, lifestyle, use of health care services and social factors, and a physical examination with measures of cardiorespiratory and morphological fitness, metabolic fitness, neck mobility, heart rate variability, and pain sensitivity. A biobank including serum, plasma, urine, DNA, and microbiome has been established, and central registry data from both responders and nonresponders are similarly available on morbidity, mortality, reimbursement of medicine, heath care use, and social factors. A complete 5-year follow-up is scheduled to take place from year 2017 to 2020, and further reexaminations will be planned. Several projects using the DanFunD data are ongoing, and findings will be published in the coming years. Keywords: functional somatic syndromes, medically unexplained symptoms, epidemiology, longitudinal cohort study, pathophysiology, risk factors