Introduction: Sexually transmitted infections (STIs) are still a main health problem all over the world, both in developed and developing countries. Individual who are at high risk of having free sex who is at risk of getting STI is in street children. Objective: To describe knowledge, attitudes, and risk behaviors regarding STIs among street children in Medan. Methods: this research is a descriptive surveillance study with a cross-sectional method involving 61 street children aged 6-18 years as respondents in Medan. Data of this research are collected by filling the questionnaire through direct interviews with respondents. The validity instruments tested by using validity construct test and reliability instrument tested by using Cronbach Alpha. Results: All respondents were not fully aware of STIs. The majority (55,7%) had a poor knowledge, 29,5% had a moderate knowledge, and only 14,8% had a good knowledge. 30 respondents (49,2%) indicate a poor attitude regarding STIs, 19 respondents (31,1%) indicate a moderate attitude and 12 respondents (19,7%) indicate a good attitude. We also found majority 52.5% had a high risk behavior, 32,7% had a moderate risk behavior and only 14,8% had a low risk behavior. Conclusion: Generally, street children had a poor knowledge, attitude and had a high risk behavior regarding STIs. .