Reactive aggression (RA) is an angry response to perceived provocation. Proactive aggression (PA) is a pre-meditated act used to achieve some goal. This study test hypotheses that (1) individuals high in RA and PA will differ in resting levels of autonomic arousal and (2) RA will be related to emotional and behavioral problems, while PA only to behavioral problems. Parents of 68 children (age 6-13) reported on child symptoms, reactive/proactive aggression, and behavior problems. Resting heart rate (HR), skin conductance (SC), and HR variability (HRV) were measured in 42 of the children. RA was significantly related to decreased HRV and a trend for decreased SC, while PA was significantly related to increased SC and HRV. RA was significantly related to increased internalizing behaviors and attention deficits, while PA was significantly related to increased hyperactivity/impulsivity and delinquent behavior problems. Findings support a distinction between child reactive (hot-tempered) and proactive (cold-tempered) aggression in autonomic, emotional (i.e., internalizing problems), and behavioral (i.e., attention deficits, hyperactivity/impulsivity, and delinquent behavior) functioning, and are discussed in relation to theories of antisocial behavior.