Epidemiological studies on the prevalence of cyberbullying and cybervictimization in different countries, using the same procedure and the same measures, are of relevance in understanding differences in results that are not due to methodological factors. The current study was conducted in 8 European countries (Bulgaria, Cyprus, France, Greece, Hungary, Italy, Poland, and Spain), involving a total of 4,847 students, using an online anonymous questionnaire (the Tabby online questionnaire). The results were analyzed by comparing differences between countries and between genders. Cyberbullying and cybervictimization were most prevalent in Bulgaria and Hungary and least prevalent in Spain. Boys committed more cyberbullying than girls in all countries, but there were no overall gender differences in cybervictimization. However, girls were more often cybervictims in four countries and boys were more often cybervictims in the other four countries. The results are discussed with regard to the importance of cross-national studies of cyberbullying and cybervictimization and the use of online data collection in order to reduce methodological bias.