Introduction: Because of young age adolescents do not have adequate knowledge of safe sex practice, appropriate contraception which increases the chance to contract a sexually transmitted infection. An important role in preventing spreading sexually transmitted infections is early sex education. Purpose: The purpose of the thesis is to present and state which sexually transmitted infections are the most common in Slovenia, and the importance of sex education in preventing them. The goals are to present and answer the following assumptions: what are their consequences on physical and mental health, how effective is early sex education and how effective are condoms. Methods: In the thesis there was used a descriptive method of work with a combination of a systematic review of scientific and professional literature written is slovene or english in the field of sexuality and sexually transmitted infections. The time frame of literature age was from 2008 to 2019. The literature was searched for through the Digital library of the University of Ljubljana (DiKUL), the Digital library of the University of Maribor (DKUM), the CINAHL bibliographic databases, ScienceDirect, the Cochraine Library, Medline, Web of Science, COBIB.SI, and in journals Obzornik zdravstene nege and Zdravniški vestnik. 35 pieces of literature were included in the analysis. Results: Most common infections in Slovenia are infections with human papillomavirus, Chlamydia trahomatis, Treponema pallidum, herpes simplex virus type 2 and the bacteria Neisseria gonorrhoeae. The vast majority of sexually transmitted infections remain asymptomatic for a long time, but when the symptoms are present, the condition can already be serious. The individual can be affected both physically and mentally. In the case of physical health the consequences can be short-term or long-term. Sex education provided early enough gives appropriate knowladge and skills to enter the world of sexuality safely. Discussion and conclusion: Sexually activity is a inevitable human desire, so it is crucial for people to understand the importance of the effects that sexually transimtted infections have on the human health, both physical and mentally. It is important to emphasize the fact that certain consequences can take from a few month to a few years to be seen, but can represent serious risks. With appropriate knowladge, advice and contraception, individuals can safely enter the world of sex and reduce the rise of sexually transmitted infections.