For the present study, AD included the following 21 illnesses identified by a recent National Institutes of Health report (1): Addison’s disease, autoimmune hemolytic anemia, autoimmune thrombocytopenia purpura, celiac disease, dermatomyositis, Graves’ disease, Hashimoto’s thyroiditis, idiopathic myocarditis, idiopathic pulmonary fibrosis, insulin-dependent diabetes mellitus, irritable bowel disease, multiple sclerosis, myasthenia gravis, pernicious anemia, psoriasis, rheumatoid arthritis, scleroderma, Sjogren disease, systemic lupus erythematosus, vitiligo, and Wegener’s granulomatosis. Persons were considered at risk for hospitalization with ICD-9 coded AD as a discharge diagnosis if they were currently enrolled in the HMO at the time of the hospitalization and the hospitalization with ICD-9 coded AD occurred between the baseline survey date and December 31, 2005.