Lee SY, et al. - Using data from the 2007–2013 Korea Youth Risk Behavior Web-based Survey of only adolescents with sexual intercourse experience (n=22,381), experts investigated the correlation between age of first sexual intercourse and the experience with sexually transmitted infections (STIs) among adolescents and to determine in which specific time period they were more likely to catch an infection from sexual intercourse. Nearly 7.4% of boys and 7.5% of girls had STI. The possibility of encountering STIs progressed as the age of first sexual intercourse was lower, for both boys and girls. Earlier start of sexual intercourse elevated the odds of experiencing STIs. As the age gap grew shorter, the odds of experiencing STIs grew. The time period of first sexual intercourse is important to consider and reinforcement of a monitoring system along with developing of other preventive strategies is needed.