In order to plan a health education programme in high schools in Southern Latium, a survey on knowledge, attitude and behaviour about Sexually Transmitted Diseases and AIDS was carried out among students of three high schools in Cassino. An anonymous, self-administered questionnaire was submitted to all students of the last two years in those schools. The results show a good knowledge of Cassino's students about HIV transmission, in similar or higher proportion respect to analogous surveys conducted in Italy or abroad. We found a good knowledge only about AIDS, Herpes genitalis and Syphilis, while knowledge about Hepatitis B, Condyloma acuminatum and Gonorrhoea is not satisfactory. Considering that 38% of male and 17% of female students declared to have already had their first sexual intercourse, the results suggest that there is a strong need to implement an educational intervention on sexuality and STD.