We identify, categorize, and score sources of uncertainty in human health and ecological risk assessments conducted for several US Army sites to identify better analytical practices and opportunities for targeted research to improve risk estimates. The reviewed assessments are from reports completed within the past 8 y and were obtained from the US Army Environmental Technical Information Center (ETIC) at Aberdeen Proving Ground, Maryland, USA. Most of the risk assessments incorporated only qualitative uncertainty analysis to demonstrate the conservatism of selected data and predictive models. Food chain transfer (e.g., concentrations of contaminants across trophic levels) dominated quantifiable sources of uncertainty across the risk assessments evaluated. Factors related to dermal exposures ranked high for human health, and effects assessment for ecological endpoints.