Immune-mediated inflammatory diseases (IMID) present a group of common and highly disabling chronic conditions that share inflammatory pathways. Several incidence and prevalence studies of IMID during the past decades have reported a considerable variation of the disease occurrence among different populations. Overall, the estimated prevalence of IMID in Western society is 5%–7%. This article provides an overview of studies of the incidence, prevalence, natural history, and comorbidities of IMID.