Studies on scientists’ practices of public engagement have pointed to variations between disciplines. If variations at the individual level are reflected at the institutional level, then research institutes in Social Sciences (and Humanities) should perform higher in public engagement and be more involved in dialogue with the public. Using a nearly complete sample of research institutes in Portugal 2014 (n = 234, 61% response rate), we investigate how public engagement varies in intensity, type of activities and target audiences across scientific areas. Three benchmark findings emerge. First, the Social Sciences and the Humanities profile differently in public engagement highlighting the importance of distinguishing between these two scientific areas often conflated in public engagement studies. Second, the Social Sciences overall perform more public engagement activities, but the Natural Sciences mobilise more effort for public engagement. Third, while the Social Sciences play a greater role in civic public engagement, the Natural Sciences are more likely to perform educational activities. Finally, this study shows that the overall size of research institutes, available public engagement funding and public engagement staffing make a difference in institutes’ public engagement.