Based on a developmental framework, a study was conducted in Portugal in two groups of youth in terms of relevant aspects related to adolescent psychosexual development: one group participated in an Experimental Project of Sex Education and Health Promotion during high school, whereas the other did not receive any formal sex education in school. Within this ex-post-facto study, the "Sex Education and Psychosexual Development Questionnaire" was administered to both groups, using the "mail-type" technique. Results reveal positive evaluations from the participants in the Sex Education Program and similarities between the groups in terms of their sexual knowledge and attitudes. However, the participants of the Sex Education Program show a multi-oriented style of sexual information and, at a behavioural level, they refer more frequently to the use of safe methods for preventing sexually transmitted diseases. The implications of these findings for sex education in schools are discussed. (Contains 3 tables and 6 notes.)