The attrition of women in academic careers is a major concern, particularly in Science, Technology, Engineering, and Mathematics subjects. One factor that can contribute to the attrition is the lack of visible role models for women in academia. At early career stages, the behaviour of the local community may play a formative role in identifying in-group role models, shaping women’s impressions of whether or not they can be successful in academia. One common and formative setting to observe role models is the local departmental academic seminar, talk, or presentation. We thus quantified women’s visibility through the question-asking behaviour of academics at seminars using observations and an online survey. From the survey responses of over 600 academics in 20 countries, we found that women reported asking fewer questions after seminars compared to men. This impression was supported by observational data from almost 250 seminars in 10 countries: women audience members asked absolutely and proportionally fewer questions than male audience members. Men and women differed in the importance they attributed to different factors preventing them from asking questions, with women rating internal factors (e.g., not working up the nerve) as more important than men. Furthermore, our observations indicated that the gender of the first person to ask a question predicted the gender imbalance in subsequent questions, with proportionally fewer questions asked by women when a man was the first to ask a question. A longer time for questions was associated with less of an imbalance, but attempts to manipulate the time for questions in two departments were unsuccessful. We propose alternative recommendations for increasing women’s visibility at these events and suggest that our results are best explained by internalized gender role stereotypes about assertiveness.