Under the perspective of the Theory of Planned Behavior, the objective of this study was to know the gender differences in the variables involved in the use of effective preventive measures in sexual relations against HIV in a sample of university students from Spain and Portugal. Furthermore, it is examined whether these factors produce different predictions concerning the adoption of safe sexual behaviour for young man and women in each country. The sample consisted of 683 university students, 319 Portuguese (64% female and 36% male) from the University of Algarve and 364 Spanish students (51% female and 49% male) from the University of Huelva. Data were obtained by means of a questionnaire. The data revealed that there are gender differences which apply in both countries, highlighting that the young women have more positive attitudes, greater perceived behavioural control and intention of condom use than young men. However, they protect themselves less that their male counterparts: the percentage of females who say using condoms as a contraceptive method is less than the percentage of males, and especially with their steady partners. The results are discussed in relation to gender role norms, to have a steady partner or not, gender relations, the associated meaning to sexual relations for men and women and their implications for the design of sexual educational programmes for them.