Background: - Adolescence is an important period in human development where a personrnreaches sexual maturity, manifest in sexual engagement; thus encountering the possibility ofrncontracting sexually transmitted diseases such as HIV/STIs. Living arrangement of adolescentsrncan expose them to risky sexual behavior increasing the chances of acquiring HIV/STIs.rnHowever, the effect of living arrangement of adolescents on risky sexual behavior has not beenrnadequately studied.rnObjective- To assess the influence of living arrangement on adolescentsâ€™risky sexual behaviorrnamong high school/preparatory students in Sebeta Town Oromia Regional State, EthiopiarnMethods â€“ School based comparative cross-sectional study was conducted in Sebeta secondaryrnschools from Dec 2015 to june 2016.A sample of 361was taken for each group (those living withrntheir family and those not living with their family).Students from governmental schools fromrngrade 9 â€“ 12 were included in the study. Data was collected using pretested interviewerrnadministered questionnaire. Descriptive and summary statistics was done. Bivariate andrnmultivariate analysis was done using logistic regression on STATA version 12.1 software tornmeasure the association of living arrangement on risky sexual behavior and identify other factorsrnassociated with risky sexual behavior.rnResults:- Seven hundren twenty two participants responded to our invitation giving response raternof 99.31%.The overall prevalence of risky sexual behavior was 27.6% (95% CI: 24.33%,rn30.89%) and it is predominant among adolescents lives away from their parents. Living awayrnfrom family was significantly associated with risky sexual practice on bivariate logistic analysisrnOR= 2.02, 95% CI :( 1.45, 2.81) but the association disappeared on multivariate analysis AOR=rn0.81 95%, CI: (0.49, 1.35). Drinking alcohols(beer) frequently(AOR=1.8, 95% CI:(1.22, 2.85),rnchewing khat(AOR=1.7, 95% CI:(1.10, 2.77),smoking cigarettes (AOR=2,95%CI:(1.07, 3.92)rnless parental monitoring (AOR= 6.1, 95% CI: (2.79, 13.52)),watching pornographyrnmovies/films(AOR=5.7, 95% CI:( (2.82, 11.10) and poor/less attachment to religiousrninstitutions (AOR=2.6, 95% CI :( 1.72, 3.91) were the factors that increase the odds ofrnpracticing risky sexual behaviour.rnxrnConclusion and recommendation: The findings of this study showed that a substantialrnproportion of Governmental secondary school-going adolescents in Sebeta are engaged to riskyrnsexual activities and that sexual activity among these adolescents aged 15-19 is influenced byrnmultiple factors,including substance use, religiosity, perceived parental monitoring and watchingrnpornography films. based on the finding of this study we suggest recommendation for programsrnworks to improve adolescent reproductive health to work on upgrading sexuality education thatrngoes beyond HIV/AIDS knowledge,to address risky sexual behavior in schools, to improvernparental role.