<sec> <title>Objectives</title> <p>This study aimed to analyze nationwide representative data from the 11^th Korean Youth Health Risk Behavior Web-Based Survey to determine whether factors including socio-demographics, smoking and alcohol consumption, were factors related to high school students that had experienced sexual intercourse.</p></sec> <sec> <title>Methods</title> <p>A total of 33,744 students (17,346 boys and 16,398 girls) in 1^st, 2^nd, and 3^rd grade at high school were analyzed. SPSS complex samples methods were used for analyses. Socio-demographic and health risk behaviors (type of region of residence, family structure, and economic status, student academic achievement, gender, high school grade, pocket money, student smoking, alcohol consumption, and having engaged in sexual intercourse) were considered as independent variables.</p></sec> <sec> <title>Results</title> <p>There were 3.6% of girls and 9.9% of boys in high school that were sexually active. This behavior and the average number of cigarettes smoked daily, and alcohol consumed weekly, represented a dose-response relationship, after considering confounding factors. Compared with students that did not smoke or consume alcohol, smoking 1–9 cigarettes per day and consuming 1–6 cups of alcohol and group “smoking more than 10 cigarettes per day and consuming more than 7 cups of alcohol, had a 5.94 and 22.25 higher risk of having had sexual intercourse, respectively.</p></sec> <sec> <title>Conclusion</title> <p>Cigarette smoking and alcohol consumption were associated with an increased likelihood of high school students engaging in sexual intercourse.</p></sec>