Negative urgency, the tendency to act rashly when distressed, is characterized by high Neuroticism, low Conscientiousness, and low Agreeableness. Because of this set of characteristics, the authors hypothesized that (1) negative urgency (NU) is a particularly important predictor of externalizing dysfunction; (2) traits that reflect primarily high Neuroticism predict internalizing dysfunction; and (3) traits that reflect primarily low Conscientiousness predict those types of externalizing dysfunction that include intense affect less strongly than does NU. In three studies, the authors showed that negative urgency concurrently predicted alcohol dependence symptoms in disordered women, drinking problems and smoker status in preadolescents, and aggression, risky sex, illegal drug use, drinking problems, and conduct disordered behavior in college students. High Neuroticism traits predicted internalizing dysfunction but predicted none of these externalizing criteria beyond negative urgency. Low Conscientiousness did not add to prediction from negative urgency, except in a few cases. The tendency toward affect-driven rash action may underlie many externalizing behaviors.