Background: Adolescents transit into adulthood with conflicting and confusing messages about sexuality and gender. They lack adequate information and preparation on sexual and reproductive health (SRH), which leaves them vulnerable to risky sexual behavior, coercion, abuse and exploitation which intern exposes them to unintended pregnancies and sexually transmitted infections (STIs) including HIV/AIDS.rnObjective: To assess the association between Comprehensive Sexual Education and Adolescents’ Risky Sexual Behavior among In School Adolescents in Addis Ababa, EthiopiarnMethod: The study used a cross sectional study design with internal comparison to assess the association between Comprehensive Sexuality Education and Risky Sexual Behavior. Gullelie sub city was purposively sampled as it was the only sub city that had Comprehensive Sexuality Education given to students. The study was conducted from November 2016-June 2017. Data were collected using structured self-administered questionnaires which was pre-tested on 30 students from non-selected but similar school in the sub city. The collected data were entered into Epi Info version 7 and cleaned before transferring the data to Stata Version 14 for analysis. Bivariate analysis was done to see the association of each independent variable with the outcome variable. Variables with P-Value of