Sleep deprivation and fatigue can have significant detrimental effects on cognitive and task perform ance during continuous operations. The current study records sleep and wake cycles, fatigue, and cognitive performance of two Marine Corps expeditionary medical teams during a 48-hour field user exercise with a realistic patient stream. The results suggest that the participants receive less than optimal sleep during the operational period, and showed changes in self-reported fatigue and risk taking. The results are discussed in light of data being collected during a field exercise. Additionally, lessons learned that can be applied to future research are described.