Most young people throughout the world will be engaged in sexual intercourse byrnage 20, whether married or unmarried (5). Study done in Ethiopia also revealedrnthat, 52.8% of high school students in North West Ethiopia to be sexually activern(3). Moreover the vast majority of sexual intercourse during adolescent arernunprotected, and therefore the risky of unwanted pregnancy, unsafe abortion, andrnSTIs including HIV/AIDS is very high for adolescents. Studies conducted so farrnon adolescent pre-marital sexual practices and factors related to it in Ethiopia wasrnfew in number and some of them were old and may not show the present reality.rnA cross sectional study was conducted to assess the magnitude of pre maritalrnsexual practices and factors related to it among randomly selected sample ofrnAmbo high school students from Jan. 2006 to Feb. 2006. Data was collected usingrnanonymous self-administered questionnaire. A total of 813 students werernparticipated in the study. About 19.4% of the respondents had experienced sexualrnintercourse. Eighty eight (56.4%) of the sexually active respondents claimed tornhave more than one sexual partners.rnAbout 16.5% of sexually active male adolescents visited female commercial sexrnworkers of which only 27.6% reported consistent condom use and 44.8% neverrnused condom during sex with female commercial sex workers. Pre marital sexualrnintercourse was associated with discussion of sex related issues with their fathersrnand age of the school adolescents. Those who discuss sex related issues with theirrnfather less practiced pre marital sexual intercourse than those who were notrn[OR=0.603(0.373, 0.975)].rnCondom use during sexual intercourse was associated with access to informationrnabout sexuality and adolescents reproduce health.rnProvision of accurate information about adolescent reproductive health, enablingrnthe community to understand adolescentsâ€™ sexuality, and establishment ofrnadolescent reproductive health club in the school is essential.