The overall goal of this two-year project is to calculate the incidence of selected systemic autoimmune diseases (SAID) in 21,786 World Trade Center (WTC)-exposed and unexposed firefighters and emergency medical service workers and to estimate the association between intense WTC exposure and SAID. This proposal originates from the WTC Program at the Fire Department of New York City (FDNY), where investigators have full access to FDNY monitoring and treatment records, excellent cohort retention rates, demonstrated ability to contact members, and accurate estimates of person-time at risk from employment records. The following SAID diagnoses will be included: systemic lupus erythematosus (SLE), antiphospholipid syndrome (APS), systemic sclerosis (SSc; both diffuse and limited), inflammatory myositis (dermatomyositis, polymyositis, or inclusion-body myositis), Sjogren's syndrome, rheumatoid arthritis (RA), and non-RA inflammatory arthritis (i.e., psoriatic arthritis and spondyloarthritis). There have been no epidemiologic studies of SAID incidence in WTC-exposed cohorts. WTC- related SAID has arisen as a concern because previous studies of non-WTC exposed workers have demonstrated increased risk after exposure to silica, dusts and chemicals, many of which were known to have been present at the WTC disaster site. Further, clinical observation of some cases triggered a preliminary record review through which we have confirmed 31 post-9/11 cases, and identified 282 potential cases requiring further review. Based on the health of the FDNY cohort and their demographic characteristics (mostly male), we would have expected fewer cases than already observed. The specific aims of this proposal are to: Aim 1: Estimate the incidence of confirmed cases of SAID in the FDNY population from 9/11/2001 until 9/10/2013; and Aim 2: Perform a nested case-control study to estimate the effect size of WTC exposure on confirmed cases of all subtypes of SAID combined