The purpose of the study was to evaluate the internal consistency and test-retest reliability of the Impulsive Aggression (IA) and Premeditated Aggression (PM) scales of the Impulsive-Premeditated Aggression Scale (IPAS) in male and female substance-dependent patients, and to compare the findings to those obtained on widely used, validated measures of aggression. Using a sample of 121 patients (61 women) in methadone maintenance treatment, 69 (35 women) of which were re-evaluated after a minimum of 2weeks, the IPAS scales showed acceptable internal consistency (alpha>.72) and test-retest reliability (ICC>.54). These results were comparable to the other aggression measures, and results among women were comparable to men. This was the first study to examine the IPAS scales in a substance use population, to contain a sufficient sample of women for sub-analyses, and to examine the stability of the measure. Findings support the internal consistency and test-retest reliability of the IPAS in male and female opiate-dependent individuals.