Introduction The risks associated with teenage sex include pregnancy and a high rate of sexually transmitted diseases (STDs). Material and methods The study compared female teenagers: 32 with STDs and 90 with fungal skin infections who were treated in the City Center for Skin and Venereal Diseases in Belgrade from January 2000 to June 2001. An anonymous questionnaire was used to collect data and an univariate logistic regression analysis was performed. Results The mean age of participants was 18.2 years. About 40% of respondents reported to have their first sexual intercourse at the age of 14-16 years. The majority of cases and controls had one or two partners, but a greater percentage of cases had six or more partners compared to controls (12.5% vs. 3.3%). Adolescents with STDs frequently had sexual intercourse on the first date (p<0.05), and more frequently reported previous STDs in their personal history (p<0.05). Consistent use of condoms was less frequent among cases than among controls, both with steady (9.4% vs. 27.8%) and irregular partners (30.0% vs. 70.6%). The majority of teenagers (95%) thinks that sexual education at schools should be better. Discussion According to the results obtained, which are in agreement with literature data, teenagers should change their behavior, especially with respect to condom use both during vaginal and anal sex. Health education at schools could probably influence future sexual behavior, and counseling for STDs should be offered to all teenagers attending STD clinics. Conclusion The best way to avoid unwanted pregnancy and STDs is to delay the first sexual experience, reduce the number of sexual partners and increase the protection by condom use.