Sleep deprivation and aggression are common problems in this society. Aggression is a complex behavior which is influenced by intrapersonal (e.g., physiology and personality) and situational (e.g., alcohol and sleep deprivation) variables. Following Berkowitzs (1990) Cognitive-Neoassociationistic model of aggression, it was hypothesized that acute partial sleep deprivation (APSD) would serve as an aversive event that would increase negative affect and override cognitive inhibition and, therefore, increase aggressive responding during the Response Choice Aggression Paradigm (RCAP) task. It was also expected that this relationship would be mediated by trait irritability and by state negative affect. Two hundred and forty undergraduate men were recruited from the departmental research participant pool and screened for factors that may contribute to potential damaging effects from APSD. Participants also completed the Profile of Mood States (POMS), the Positive and Negative Affect Schedule (PANAS), the Caprara Irritability Scale (CIS), the Sleep Habits Scale (SHS), and the Brief Michigan Alcoholism Screening Test (B-MAST). Of those screened, eighty-nine were invited to participate in the laboratory session. Half were assigned to the experimental APSD group and were instructed to limit their sleep to 4 hours the night prior to the session, and half were assigned to the control group and instructed to sleep their normal amount. At the laboratory, participants completed the POMS and PANAS and participated in the RCAP. Seventy-three participants were included in analyses. Participants in the experimental group scored higher at the laboratory session on the Tension-Anxiety and Fatigue-Inertia subscales and lower on the Vigor-Activity subscale of the POMS and the Positive Affect subscale of the PANAS than at the screening session. It was found that participants in the experimental group evinced higher aggression (i.e., higher shock frequency and flashpoint duration). The effect of APSD on shock frequency was mediated by subjective fatigue. Additionally, trait irritability was positively correlated with the proportion of highest shocks administered but could not be tested as a mediating variable between APSD and aggression. Results were consistent with the Cognitive-Neoassociationistic model of aggression and demonstrate potential deleterious effects of sleep deprivation in our society.