Dynamic warning messages are a harm minimization strategy aimed at preventing or reducing gambling-related problems by assisting individuals to make informed choices about their gambling. Laboratory studies have demonstrated the efficacy of dynamic warnings in facilitating responsible gambling. This article presents the results of a trial of the related effectiveness of dynamic warnings appearing either in the middle or on the periphery of electronic gaming machines (EGMs) screens in commercial gambling venues. Regular gamblers (n = 667) were surveyed to assess their recall of warning messages and the perceived impact of message placement on thoughts and behaviours. Messages appearing in the middle of screens were recalled to a greater extent, and respondents reported that these were more impactful and useful than messages on the periphery of screens. As one of the first trials of dynamic warning messages in operating EGM venues, the results provide important verification and validation of previous laboratory research. Results demonstrate that dynamic warning messages appearing in the middle of an EGM screen during play are likely to be a more effective harm minimization intervention than messages on the periphery of EGM screens.