Many large-scale cross-national studies rely on a single-item measurement when comparing prevalence rates of traditional bullying, traditional victimization, cyberbullying, and cyber-victimization between countries. However, the reliability and validity of single-item measurement approaches are highly problematic and might be biased. Data from three countries were used as an example case to compare the single- and multiple-item approaches from a substantial and a statistical point of view. The sample comprised 671 Austrian (46.3% girls), 691 Cypriot (45.9% girls), and 604 Romanian (46.7% girls) 12 year old students. Data were collected via self-assessments with single and multiple-items. Because scalar measurement invariance could be established for the multiple-item measurement approaches, latent means between the three countries were compared. Substantial results of the single- and multiple-item approach did not differ for traditional bullying and traditional victimization, but differed for cyberbullying and cyber-victimization. As a consequence, we suggest using carefully validated multiple-item scales for cross-national comparisons.