Rates of Internet usage among Vietnamese students have been estimated to be high and consequently, risk for cyber-bullying and cyber-victimization also may be high. However, current research in this area is limited, with the two primary studies of cyber-bullying among Vietnamese students based on short questionnaires (three and four items) and limited samples (i.e., from one school, and from two schools in the same city). A more comprehensive assessment thus is important in order to more precisely define the magnitude of the problem and to more accurately identify culturally relevant risk factors. In the present study, 1,040 Vietnamese 6th through 12th-grade students from 4 schools in Hanoi and Ho Chi Minh City were assessed using the Revised Cyber Bullying Inventory. Results indicated that 7.1% of participants were victims of cyber-bullying only, 4.7% were initiators of cyber-bullying only, and 11.3% were both initiators of cyber-bullying and victims of cyber-bullying; thus, about one-fourth of the sample was involved in maladaptive online behaviors. Academic achievement was significantly related to levels of cyber-bullying but not cyber-victimization, with top-performing students showing significantly higher levels of cyber-bullying than all other students. Implications of these results are discussed.