Sex education in Portugal has become a right and an obligation starting in the first years of school. However, despite being required by legislation, this is not easy to achieve, partly because of weaknesses in the training of teachers, which need to be identified. In this study, data were collected about the knowledge, behaviours and beliefs of 148 teacher trainees of elementary education (6-10 years old) from two Portuguese public higher education institutions. The topic of sexuality and human reproduction had been covered by almost all of them during their initial training and was considered important by most of them. Nevertheless, about 85% asserted they are not confident enough to teach this topic to small children in a classroom and committed scientific errors about physiological-anatomical aspects of the human body. All subjects felt that there is a lack of specific didactic materials, which does not help to overcome those obstacles. It was also possible to identify in these future teachers risky sexual practices resulting, in part, from their beliefs, which could have implications about the way the topic will be approached in the classroom. These findings show how essential it is for training institutions to pay greater attention to the education of future elementary school teachers in this area. (Contains 4 notes.)