The well-documented negative association between serum cholesterol and aggressive behavior has led Kaplan to propose a cholesterol-serotonin hypothesis of aggression. According to this hypothesis, low dietary cholesterol intake leads to depressed central serotonergic activity, which itself has been reported in numerous studies of violent individuals. In the present study, 25 violent psychiatric patients participated in a microbehavioral experience sampling procedure to examine differences in self-reports of affective and cognitive experiences as a function of serum cholesterol concentrations. For 7 days, they wore signaling devices that emitted an average of seven signals a day. Following each signal, patients filled out a mood questionnaire. Total serum cholesterol (TSC) concentration was positively associated with measures of affect, cognitive efficiency, activation, and sociability, suggesting a link between low TSC and dysphoria. These findings are consistent with the cholesterol-serotonin hypothesis and with the substantive literature linking both aggression and depression to depressed central serotonergic activity.