Until relatively recently, the pathophysiologic significance of the recognized associations between autoimmunity and swelling was largely unknown. It has now become clear that autoimmunity can play a critical role in the pathogenesis of chronic urticaria and acquired C1-INH deficiency with angioedema. Chronic urticaria has been associated with antithyroid autoantibodies, anti-IgE autoantibodies, and anti-Fc epsilon RI autoantibodies. The latter two autoantibodies are particularly interesting in that they have been shown to be capable of directly causing mast cell degranulation. It appears likely, therefore, that most cases of chronic urticaria will ultimately be considered an autoimmune disease rather than an allergic disease. The link between autoimmunity and the development of acquired C1-INH deficiency is also of interest. Recent studies suggest that the majority of acquired C1-INH deficiency patients have anti-C1-INH autoantibodies that appear to be responsible for the development of the C1-INH deficiency. In addition, both chronic urticaria and C1-INH deficiency can be associated with other autoimmune diseases, although the importance of these associations remains to be determined. Recognition of the role of autoantibodies in the pathogenesis of chronic urticaria and acquired C1-INH deficiency has altered the range of diagnostic and therapeutic approaches that need to be considered in approaching patients with chronic urticaria or acquired C1-INH deficiency. Future progress in understanding the genesis of these diseases may help elucidate the mechanism of autoantibody generation.