Research on gender-based violence (GBV) is an important tool for assessing the scale of crime, especially the phenomenon of violence. International studies to date have focused primarily on violence against women. The first of these, IVAWS (International Violence Against Women Survey), was intended as a challenge to scientists, law enforcement agencies and NGOs. Another European study on violence against women was conducted by the FRA (Fundamental Right Agency). Eurostat is currently planning a new GBV study, which is more comprehensive because violence against women and men will be considered. This study faces new methodological challenges. The GBV project covers various forms of violence, from domestic violence to violence at work, online, mobbing, etc. The first stage is the so-called pre-test, and the pilot was implemented in several EU countries, including Poland. Basic research is planned for 2022 in all European Union countries. The basic GBV research tool is a questionnaire whose questions include the intensity of various types and forms of violence against women and men. In the interpretation of the results, especially in an international perspective, attention should be paid to the differences in the perception of violence by victims, as well as in the scale of reporting violence. The differences also concern the causes, forms and consequences of violence. How can discrepancies in the size and conditioning of gender-based violence be assessed? This article presents methodological issues and experiences related to the implementation of these pilot studies.