Individuals differ along a continuum of preference for diurnal activity level, known as Morningness-Eveningness. Individuals low in Morningness traits, i.e., preferring later awakening and bed times, have been shown to score higher on personality traits of impulsiveness and novelty-seeking. No studies have yet examined the association between Morningness-Eveningness and the related construct of risk-taking. Therefore, the present study examined (1) whether Morningness was correlated with self-reported and behavioral measures of risk-taking, and (2) whether one night of sleep deprivation would produce changes in risk-taking and sensation-seeking. 54 healthy adults were administered the Morningness-Eveningness Questionnaire at intake, and administered the Brief Sensation Seeking Scale, Evaluation of Risks Scale, and Balloon Analog Risk Task at rested baseline, again following 23 hr. of sleep deprivation, and finally after a 12-hr. period of recovery sleep. Lower Morningness scores were associated with higher self-reported total risk-taking propensity when rested (p< .05) and sleep deprived (p<.005), but correlations were not significant for sensation seeking or actual risk-taking behavior. Relative to baseline and postrecovery periods, sleep deprivation significantly reduced risk-taking propensity, including self-report indices of self-control, danger-seeking, energy level, and sensation-seeking, and behaviorally measured risk-taking. Chronotype did not interact with sleep condition for any of the dependent variables, although Evening Types scored higher on several indices of risk-propensity. Findings suggest that Morningness traits are inversely related to greater risk-taking propensity, while sleep deprivation significantly reduces self-reported and behaviorally demonstrated willingness to engage in high-risk and sensational activities under conditions of uncertainty, regardless of chronotype.