Th e presented study presents results of research conducted in 2015 within the project of the Ministry of Education, Science, Research and Sport of the Slovak Republic VEGA No. 1/0244/15 Detection and Resolving Cyber-Bullying. Th e aim of the research was to fi nd out and analyze levels of cyber-bullying severity. Participants in the research were 1118 respondents 11-18 years old (average age 15.25, SD 2.55) across the Slovak Republic. Th e severity of cyber-bullying was assessed through the GRM (Graded Response Model). Th e most severe forms of cyber-bullying were posting a mean video, creating a hurtful web-page and threats of bodily injury sent through a text message. Th e least severe forms were mean comments on the Internet, spreading rumours and posting mean or hurtful photographs of others.