The thyroid gland is the most common organ affected by autoimmune disease. Other autoimmune diseases, most notably type 1 diabetes mellitus, are increasing in incidence. It is unknown whether autoimmune thyroid diseases are following the same pattern. This review summarizes studies of autoimmune thyroid disease incidence and prevalence since 1950, not only for these measures of occurrences, but also for commenting on identified risk factors for thyroid autoimmunity. We find that incidence of autoimmune thyroid disease is currently higher than in historic series although the studies are so variable in design, patient population, disease definition, and laboratory methods that it is impossible to tell whether this difference is real. Further research is required to assess the possibility of changing disease patterns of autoimmune thyroid disease as opposed to simple changes in diagnostic thresholds.