The aim of this study is to discover the prevalence of cyberbullying among adolescents from Ecuador and Spain, and identify any differences by gender, school year, and ethnic-cultural background. A culturally-diverse group of 33,303 adolescents took part in the study (Ecuador = 10,918; Spain = 22,385). Our results show that in Ecuador, one in four, and in Spain, one in five teenagers were involved in cyberbullying. In both countries, teenagers in the higher school years were more commonly involved. Significant differences in gender and role of involvement were detected in both countries. In Ecuador, no differences were noted between the different ethnic-cultural groups as regards to the roles of involvement in cyberbullying. However, in Spain, these differences do exist. In this paper, these findings are discussed, and proposals for how to prevent cyberbullying are given.