Background: Each time a deployed military member has an exacerbation of a pre-existing chronic disease there is a potential risk to mission success, individual health, and the safety of the unit. Currently, North Atlantic Treaty Organization (NATO) member nations employ different approaches to assessing an individual's medical fitness for deployment. Objective: To set the minimum medical standards for NATO deployments. Methods: A seven nation task group met periodically from 2008 to 2012 to develop guidelines for frontline military physicians to assess medical fitness for deployment. Results: A medical deployment guide for 31 specific diseases/conditions using a rational, standardized and algorithmic approach based on a red–yellow–green risk stratification. Conclusions: If adopted as a NATO policy, this guide could then be kept up-to-date through a process that allows nations to track individuals with known chronic disease who were deployed into a theater of operations, allowing the guide to become increasingly evidence-based, and also more accurate in quantifying the risk of exacerbation based on individual and disease characteristics, as well as the nature and length of the deployment.