Background: Premarital sexual behavior was big problem for adolesence in Indonesia. The data show that the highest adolesence sexual behavior is in Yogyakarta. The impact of premarital sexual behavior of adolesence is HIV/AIDS, pregnancy before married, sexually transmitted diseases and death. The most dominant factor of premarital adolesence sexsual behavior is peer group influence. Research Objective: To know about correlation between peer group with premarital sexual behavior among adolesence in SMAN Y Yogyakarta. Methodology: This research is a type of quantitative research design correlation that has the purpose to reveal the relationship between variables. This research used the design of cross sectional. Sampling method used is simple random sampling as much as 114 people and already meets the criteria of inclusion and exclusion. Instrument in this research used questionnaire. This research used the correlation sperman rank test. The Results: Based on Sperman Rank Test, get the results p value = 0,000 (p<0,05) which means there is significant relationship between the friends of the same age towards premarital sexual behavior in teenagers who are school in Y High School Yogyakarta. Conclusion: There is a correlation between peer group with premarital sexual behavior among adolesence in SMAN Y Yogyakarta..