Marksmanship performance is a challenging skill for recreational enthusiasts, sport competitors and tactical (military and law enforcement) athletes. Peak performance is associated with the favorable psychological state of 'flow,' occurring when we perceive equilibrium between challenges and our capabilities. Stressors, like sleep loss, disrupt marksmanship performance and may also degrade the experience of flow. We examined the effects of sleep restriction on flow state and marksmanship performance. U.S. Army Soldiers (n=15, Mean age=21.2 years, SD=3.5) conducted a rifle marksmanship task on a simulator followed by the Long Flow State Scale 2 -- Physical (FSS-2). Four sessions were conducted including a well-rested baseline session on the first day of the study, and then again at 20, 44 and 68 hr into sleep restriction. Overall flow summary score and five subscale components of flow degraded significantly by 44 hr of sleep restriction. The longer the duration of weapon firing each day, the greater the decline in flow. Lower overall flow scores were associated with slower trigger pull (Pearson r(13) = -.59, p = .02) and slower general reaction time (r(13) = -.64, p =< .01), with significant degradation at 68 hr of sleep restriction. Higher overall flow state scores positively correlated with the ability to correctly identify enemy from friendly targets at 68 hr (r(13) = 0.53, p = .04). Our data suggest that marksmen whose flow is less disrupted by sleep restriction may also perform more timely and with less errors in decision making. [ABSTRACT FROM AUTHOR]