Little is known about the health effects from oil spills on response workers, despite the frequency of these events worldwide. The Deepwater Horizon (DWH) disaster, which released approximately 200 million gallons of crude oil into the Gulf of Mexico, was the largest oil spill in U.S. history. The unprecedented interagency response, led by the U.S. Coast Guard, involved over 7,000 Coast Guard workers, who carried out a wide range of response/clean-up activities. Of the few studies which have evaluated the human health consequences of oil spills, almost all have been cross-sectional. Respiratory symptoms, including cough and shortness of breath have been consistently reported among these studies. The longest follow- up to date of clean-up workers found lower respiratory tract symptoms persisting two years after response work ended. Other studies have found neurological, hematologic, psychological, genotoxic and endocrine effects. Additionally, benzene, a major component of crude oil, is a known hematotoxin and carcinogen, even at low exposure levels. Long-term studies of oil-spill responders are urgently needed. We propose a study of a cohort of Coast Guard DWH responders to elucidate the health consequences of oil spill exposures by capitalizing on valuable, existing military data. The key sources of existing data for this study include an exit survey completed by each responder, which provides self-reported exposure and health data; personal monitoring data on a subset of responders; objective clinical data in the form of Coast Guard electronic health records (EHRs) and ICD-9 coded surveillance data, which will enable pre- and post-spill comparisons; and serum samples of Coast Guard responders, which will provide DNA for genotyping. In addition, members of certain high risk occupations are enrolled in a surveillance program with more intensive periodic examinations, thus providing more detailed and comprehensive EHR data. These sources of objective health/bio-specimen data are collected and used by the military solely for individual clinical care or surveillance, but they will be invaluable for the proposed epidemiologic analyses. The objective of the proposed study is to identify health effects in the Coast Guard DWH responder cohort by analyzing data from the exit survey and by comparing pre- and post-DWH disease rates based on objective health data such as Coast Guard EHR entries and ICD-9 codes. The proposed Coast Guard cohort study has the ability that no other study to our knowledge will have to compare objective health data, post-spill to pre-spill. Additionally, it will efficiently lay the groundwork for future nested case-control studies of selected outcomes and for the targeted study of biomarkers of adverse biological effect using valuable pre- and post-spill serial serum samples. By carefully following up this cohort we may be able to prevent or mitigate long-term health consequences among these workers and provide much-needed information to help prevent adverse health effects in future oil spills.