Objective: To describe injuries and illnesses presented and profile mood states and sleep patterns during a desert environment ultramarathon. Design: Prospective study gathering data on mood states and injury patterns. Setting: Gobi Desert, Mongolia. Participants: Eleven male competitors (mean mass, 83.7 +/- 7.1 kg; body mass index, 24 +/- 1.79 kg/m2; age, 33 +/- 11 years). Interventions: Injuries were clinically assessed and recorded each day. Main Outcome Measures: Mood state was assessed using the Brunel Mood Scale. Results: All subjects presented with abrasion injuries, dehydration, and heat stress. Vigor decreased over the first 6 days while fatigue increased (P <0.05). Fatigue and vigor recovered on the final morning. The observed recovery was set against increasing levels of depression, tension, and confusion, which peaked at days 5/6 but returned to day 1 levels on the 7th day morning (P <0.05). Mean sleep duration (6:17 +/- 00:48 hours:minutes; lowest on day 6, 4:43 +/- 01:54 hours:minutes) did not vary significantly across the 7 days but did correlate with mood alterations (P <0.05). Increased anger and fatigue correlated strongly with sleep disruption (r = 0.736 and 0.768, respectively). Vigor and depression displayed a moderately strong correlation to sleep (r = 0.564 and -0.530). Conclusions: Injury patterns were similar to those reported in other adventure/ultradistance events. Consistent with previous work, data show increased fatigue and reduced vigor in response to an arduous physical challenge.