The Department of Veterans Affairs requested that the Institute of Medicine of the National Academies of Sciences, Engineering, and Medicine conduct a study to respond to Public Law 110-389 enacted in 2008 to determine the incidence and prevalence, as well as the risk of developing multiple sclerosis and other neurologic diseases as a result of service in the 1990-1991 Persian Gulf and post 9/11 Global Operations theaters. Specifically, the other neurologic diseases to be considered are migraines, Parkinson’s disease, and brain cancers, as well as central nervous system abnormalities that are difficult to precisely diagnose. The committee reviewed literature on burden of illnesses; examined available data sources for suitability in executing the proposed study; scrutinized possible algorithms to assist in characterizing diseases in a study; and assessed the utility of a study based on available Department of Veterans Affairs (VA) data. In examining the burden of illnesses, the committee found that the existing data suggest that Gulf War deployed veterans do not have a higher prevalence of the diseases of interest than the nondeployed Gulf War veterans, with the exception of headache and migraine. The burden of illness in the post-9/11 veterans cannot be compared to the nondeployed, as almost the entire cohort of those veterans has been deployed. Moreover, the VA survey data and administrative databases alone are inadequate for assessing the effects of deployment, as they are limited to users of VA health care, which comprise only 36% to 60% of the entire veteran population of interest. Therefore, while technically feasible to conduct a study as outlined in the committee’s statement of task, the committee decided not to proceed with the study because it would be limited to using existing VA data (as stated in the VA contract with the Institute of Medicine of the National Academies of Sciences, Engineering, and Medicine), it would repeat the work of others, and it likely would not advance the knowledge significantly beyond what is already known. However, if additional data were made available, then a rigorous study likely could be conducted that advances knowledge on these issues.