Sexually transmitted diseases among youths is a growing problem. Generally, the knowledge about sexually transmitted diseases is relatively good, however, the risktaking among youths is great. The schools education regarding sex is often insufficient. The foundation for avoiding STD is knowledge. However, knowledge does not solve the attitude problem regarding the use of condoms. The purpose of our study was to describe the knowledge of older teenagers regarding STD, the sexual education in high school, and the youths attitude towards the usage of condoms. High school seniors were selected as respondents. This study uses a quantitative method. A survey was performed to collect data since the subject might be considered sensitive. The survey was distributed to 189 students of which 175 answered the survey. The result shows that schools are the biggest source of information regarding sexual education. Also, the results show that women, more often than men, are exposed to the risks of being infected with STD. To highlight the importance of preventive work for youths sexual behavior, we believe that school is a very important place. In conclusion, a good system for teaching about sexually related topics in school is very important in order to decrease the risky behavior of the youth.