As of April 2003, 64,801 HIV cases have been documented in Vietnam (Policy Project 2003), 53.9% of which are among individuals 20-29 years of age. Although HIV education efforts have increased, there remains a need for proven effective programs. We present findings from a randomized-controlled effectiveness trial of an HIV prevention program for adolescents 15-20 years. Four hundred eighty adolescents were randomized into control and intervention groups. Evaluation data were collected using the Vietnamese Youth Health Risk Behavior Instrument, including scales based on the protection motivation theory (PMT). Findings presented show significant differences in knowledge of severity and vulnerability of HIV/AIDS (p less than 0.05), perceptions of self-efficacy (p less than 0.001), and response efficacy for condom use (p less than 0.05) between control and intervention youth at immediate and 6-month postintervention. A significant difference was also found for response cost of condom use (p less than 0.05) at immediate postintervention. No significant difference was found for the construct of response cost at 6 months, and there were no significant differences for the constructs external and internal rewards. Reported engagement in vaginal sex (1.7%), or anal and/or oral sex (3.1%) was extremely low, and therefore changes in actual behaviors could not be accurately measured. However, intention to use condoms in possible future sexual encounters increased significantly (p less than 0.05) for the intervention youth compared to control youth between baseline (74/240, 30.8%) and both immediate postintervention (132/230, 57.4%), and six month follow-up (123/228: 53.9%). These data suggest the potential applicability of the PMT for HIV program development with non-Western adolescents but also point to the need for further studies on how constructs within behavioral theories might need to be modified in different sociocultural settings.