The objective of this study was to explore differences inrnknowledge about HIV/ AIDS and risk reduction behavior. For thisrnpurpose a self administrative questionnaires was administered torn233(121 male and 112 female)students in Dejach Wondrad HighrnSchool in Yeka Sub City, Addis Ababa. The result showed that arnsignificant(p=0.05) difference in knowledge score was found as arnresult of sex, age and two interaction effect sex by age and threerninteraction sex by age by grade level. But the remaining factorsrnwere unable to serve as sources of variability. A statisticalrnsignificant difference shows due to grade by sex interaction inrnrisk reduction behavior. But all remain was not significant. Inrnaddition, the correlation between knowledge about HIV/ AIDS andrnrisk reduction behavior was 0.07. Which implies change inrnbehavior and personal concern due to the appearance ofrnHIV / AIDS were very small.