Males parolees were recruited into a laboratory study to determine the relationship between their previous criminal history (violent versus nonviolent), and behavioral and psychometric measures of impulsivity. During sessions, subjects were given two response options defined as: 1) an impulsive choice--small monetary reward after a short fixed delay; and 2) a self-control choice--a larger monetary reward after a variable longer delay. Based upon an extensive experimental literature in animals and humans related to delay of gratification, the degree of impulsivity was defined as the proportion of trials on which the subject selected the impulsive option. Our results indicated that the violent subjects selected the impulsive option significantly more often than the nonviolent parolees. The number of impulsive responses parolees emitted was significantly correlated with the number of aggressive responses reported in an earlier paper. This study provides support for the relationship between impulsivity and aggression among male parolees.