Background: Foot friction blisters in military personnel lessen a soldier's mobility, concentration, and critical decision-making skills.1-4 Objective: To determine the prevalence of and factors associated with friction blisters during deployment in all military personnel who nonurgently presented to the 28th Combat Support Hospital. Methods: A cross-sectional survey was performed at the 28th Combat Support Hospital. Statistical tests used included descriptive statistics, chi-square tests, and logistic regression for nominal data. Results: The response rate was 97% with 872 surveys completed. Blister prevalence was 33% (95% confidence interval [CI] = 30.0-36.4). Eleven percent of these sought treatment (p < 0.001). Factors increasing the risk of developing blisters include female sex (prevalence ratio [PR] = 1.55, 95% CI = 1.27-1.91), wearing boots not broken in (PR = 1.52, CI = 1.26-1.85), longer than 6 months in theater (PR = 1.33, CI = 1.09-1.63), and history of prior blisters (PR = 2.08, CI = 1.69-2.56). Conclusions: The prevalence of foot friction blisters was 33% during a 12-month block of Operation Iraqi Freedom I. Of these, 11% required medical care. The group most likely to develop blisters is women, ages 26 to 34, who are unable to break in their boots and have a past history of blisters.