Autoimmune diseases are conditions in which the immune system damages normal components of the individual. Some estimates indicate that more than 20% of the population suffer from one or another autoimmune disease. Ten key points are briefly reviewed in this article to emphasise the significance of autoimmune diseases in health care. These include, among others, the great variety and worldwide distribution of these conditions, the clinical importance of some of these diseases such as systemic lupus erythematosus, the antiphospholipid syndrome, Sjögren's syndrome or systemic sclerosis, or the relationship between autoimmunity and virus infections, atherosclerosis, malignancy and Psychiatry.