Objective: Sleepiness (the propensity to fall asleep) and fatigue (physical and cognitive lethargy), while related, are two distinct constructs that may differentially impact cognitive functioning; however, few studies have concurrently examined these factors. The goal of the present study was to examine the independent contributions of fatigue and sleepiness to measures of impulsivity, executive functioning, and planning. Method: Participants were healthy young adults (N = 96) who completed the Baratt Impulsiveness Scale (BIS-11) which assesses attentional, motor, and non-planning impulsivity, the Stanford Sleepiness Scale, and the Profile of Mood States (POMS) fatigue subscale. Additionally, participants completed the Zoo Map and Maze Tasks as measures of planning abilities and Trails A and B as a measure of executive functioning. Results: To assess the relationships between sleepiness, fatigue, and cognitive functioning, linear regressions were conducted with sleepiness and fatigue simultaneously entered as predictor variables and variables of impulsivity, executive functioning, and planning as outcome variables. Results indicated that sleepiness (b = 1.97, SEb = .98, p = .05) and fatigue (b = .42, SEb = .21, p = .04) were associated with BIS total scores. Fatigue was associated with attentional impulsivity (b = .19, SEb = .06, p = .004) and maze solve total (b = .98, SEb = .49, p = .05). There was a trend toward an association between sleepiness and Trails A completion time (b = 1.46, SEb = .78, p = .06). Conclusion: Fatigue and sleepiness may be differentially associated with aspects of cognitive functioning. Future studies should continue to assess the impact of both sleepiness and fatigue, as interventions to decrease the impact on cognitive functioning may differ.