Introduction:
The sexual health of adolescents depends to a great extent on prevention through informing them by applying school programs of Sexual Education. Through them we can upgrade their knowledge, convince them to adopt healthy sexual behaviors and shape conscientious people.

Purpose:
The study aims to investigate the knowledge of secondary school teachers regarding the sexual health of adolescents and to highlight the necessity of organizing educational programs to improve them in this matter, in order to provide valid and timely information to adolescents.

Material and Methods:
The research was carried out with a structured questionnaire. Samples were first pilot tested and the value of the Cronbach alpha index was calculated which highlights its reliability since it was equal to 0.72. Statistical analysis was performed with the IBM SPSS Statistics 26.0 program, where the frequency, percentage, median and interquartile range were calculated for the Likert-type questions, while the frequency and percentage were calculated for the categorical variables. Investigating whether a quantitative variable differed between two levels, a t-test was used, and to investigate correlations between quantitative variables, the value of the Pearson linear relationship coefficient was calculated. The level of statistical significance for all controls was 5%.

Results:
192 teachers participated in the survey with an average age of 48.04 years and 64.40% women. The average length of service was 15.14 years and 39.60% worked in schools in the Attica region. 83.20% need additional training and 90.80% want training seminars. 85.70% consider that Sexuality Education should be taught by qualified teachers, 83.50% by health teachers and 77.20% by health professionals. The level of knowledge between teachers of the health sector and those of other specialties differs (t (156) = -3.61, p<0.001), with the former having a higher level of knowledge. The level of knowledge in children's psychosexual development also differs between teachers who have attended a training program related to Sexuality Education and those who have not (t (156) = - 2.35, p=0.020), with the former again to have a higher level of knowledge.

Conclusions:
In conclusion, the findings of the research reinforce the importance of the existence of Sexual Education in the educational work and the teachers themselves recognize that they are the first line of intervention since they need training in order to effectively cope with its teaching. Collaboration with health professionals, such as doctors and midwives, could be beneficial both in conducting training seminars for teachers and co-teaching the Sexuality Education course. Health professionals, especially midwives, are already active and organize updates in the context of prevention and health education since they belong to Primary Health Care.