Objective: The study of intimate partner violence has long been a funding priority and a focus of research, necessitating the assessment of aggression with large samples. In response, online assessment has become increasingly common, particularly when studying college students. However, it is unclear whether measures of partner aggression can be reliably and validly administered online. The purpose of the present study was to investigate the psychometric equivalence of written and Internet formats of questionnaires commonly used in the study of partner aggression to inform researchers considering a transition to online data collection. Method: Self-report questionnaires assessing psychological and physical aggression as well as measures of related interpersonal and intrapersonal constructs were administered to 169 young adults in committed dating relationships. The same measures were administered twice via written and/or online methods over a 2-week period. Method order was counterbalanced among participants and temporal stability was controlled. Results: Measures of aggression generally demonstrated psychometric equivalence across methods with few exceptions. Conclusions: Results support the use of online versions of the CTS2 and MDEAS, and highlight the utility of collecting aggression data online. Results suggest that participants may provide more reliable and dependable responses under conditions of perceived anonymity afforded by online administration of aggression questionnaires. (PsycINFO Database Record (c) 2015 APA, all rights reserved)