In this study, the authors developed the Adult Scale of Hostility and Aggression Reactive-Proactive (A-SHARP). Sixty-one caregivers rated 512 individuals with intellectual and developmental disabilities on the A-SHARP. Exploratory factor analysis revealed 5 factors on the Problem Scale: (a) Verbal Aggression, (b) Physical Aggression, (c) Hostile Affect, (d) Covert Aggression, and (e) Bullying. Internal consistency was high, and intercorrelation of subscales suggested logical convergent and divergent validity. Separate scores were also derived for the Provocation Scale, which was developed to reflect motivation for the aggression (reactive vs. proactive). Analyses of demographic variables revealed 1 gender effect, several effects due to age and functional level, and no effect of ethnicity. Normative data are provided for the Problem Scale.