BACKGROUND፡ Street youth are exposed to situations that make them vulnerable to sexual and reproductive health problems. The majority of street youth are living in conditions of severe deprivation, which place them at all kinds of health risks. Street youth have risky sexual behaviors that increase the likelihood of adverse sexual and reproductive health consequences. Therefore, this study aimed to identify the prevalence and associated factors of risky sexual behavior among street youth in Dilla town, Gedeo zone, South Ethiopia, 2018.METHODS: A cross-sectional study was conducted among 279randomly selected street youth after locating and identifying them through census using a structured pre-tested questionnaire. Descriptive and binary logistic regression analyses were used. Statistically significant was declared at alpha<0.05.RESULTS: The prevalence of risky sexual behavior among street youth in Dilla town was53.9% (95% CI –(48, 60.2)). Female sex (AOR=9.57, 95% CI- (1.76, 52.07)), age (AOR=1.23, 95% CI- (1.08, 1.39)), educational level (AOR=3.00, 95% CI- (1.08, 8.33)) and alcohol intake (AOR=2.27, 95% CI – (1.11, 4.68)) were statistically significant with risky sexual behavior.CONCLUSION: A substantial number of street youths were engagedin risky sexual behavior, while female sex, increase in age, educational level, and alcohol intake of street youth were found to contribute to aggravate the problem. This calls formobilizing interventions considering the above factors to bring behavioral change in reducing risky sexual practices.KEYWORDS: Risky Sexual Behavior, Street Youth, Ethiopia