Physical aggression harms individuals, disrupts social functioning across multiple forms of psychopathology, and leads to destruction within communities. Physical aggression is associated with aberrations in the interpretation of ambiguous information. However, the specific cognitive mechanisms supporting this link remain elusive. One potentially relevant cognitive mechanism is reflection impulsivity, the amount of information gathered during decision-making. Reflection impulsivity characterizes how individuals resolve ambiguity in the process of forming judgments when multiple interpretations of a stimulus are possible. In a sample of 98 incarcerated men, we examined reflection impulsivity using a novel social information sampling task. The primary aim of the study was to investigate the relationship between physical aggression and social reflection impulsivity. Additionally, we assessed the frequency of different social judgments (hostile vs. benign), the extent to which reflection impulsivity varied in the context of these different social judgments, and subjective certainty about social judgments. Finally, we investigated whether social reflection impulsivity moderated the relationship between physical aggressiveness and violent crime. Results indicated that more physically aggressive individuals displayed heightened social reflection impulsivity, which was amplified in the context of hostile judgments. Moreover, more physically aggressive individuals were more certain about their hostile judgments and more certain when judgments were made with unconstrained access to behavioral information. Finally, impulsive hostile judgments in physically aggressive individuals related to a more extensive history of assault charges. These findings suggest that physically aggressive individuals exhibit deficits in information gathering, leading to ill-informed and inflexible social judgments. (PsycINFO Database Record (c) 2019 APA, all rights reserved).