The study aimed to analyze sex differences in cyberbullying, with a sample of 3,026 participants from the Basque Country (Spain), aged from 12 to 18 years, 51.5% female and 48.5% male. The Cyberbullying Test was administered (Garaigordobil, 2013) to assess the frequency with which 15 behaviors had been received, performed and observed during the past year, and obtaining four psychometric indicators: victimization, perpetration, observation, and aggressive victimization. It was found a significantly higher percentage of female victims (female= 17.6%, male= 12.5%), although the average of behaviors in both sexes was similar. The percentage of perpetrators was similar (male= 7.8%, female= 7.7%), although the average behavior of perpetration was significantly higher in males. The percentage of aggressive victims was similar (male= 5.2%, female= 5.1%), and the mean of behaviors that had been received/performed was also similar. The percentage of female observers was significantly higher (female=38%; male= 27.1%), and the mean of behavior observation by females was also higher. The study provides prevalence rates of cyberbullying in the Basque Country, and supports the need for prevention and intervention.