--- - |2+ The most studied bimodal classifications of aggressive behavior are the impulsive/premeditated distinction measured with the Impulsive Premeditated Aggression Scale and the reactive/proactive distinction measured with the Reactive Proactive Questionnaire. The terms of these classifications are often used interchangeably, assuming that reactive aggression is equivalent to impulsive aggression and that proactive aggressive behavior is the same as premeditated aggression. The correspondence or discrepancy between both aggression classifications/questionnaires, however, is understudied. Therefore, the current study investigated the correspondence between the RPQ and IPAS in a sample of 161 forensic psychiatric outpatients (FPOs) with severe aggressive behavior. Correlation analysis revealed a limited correspondence between the RPQ and IPAS. Cluster analyses derived three clusters from the RPQ as well as the IPAS: these clusters did not match in 60.3% of the cases. Furthermore, the notion that the RPQ measures trait aggression whereas the IPAS assesses state aggression could not be verified. The present study indicates that aggression subtypes as measured by use of the RPQ and IPAS correspond only partially and should not be used interchangeably. Furthermore, it was suggested that RPQ focuses more on actual aggressive behavior and the IPAS more on emotions and their regulation. Future research is needed to elucidate the applicability of both questionnaires in further detail. - Aggressive Behavior, Volume 44, Issue 5, Page 471-480, September/October 2018.