Relationships and sexuality education (RSE) was introduced in Irish schools in 1995 to address pressures on young people specific to relationships and sexuality. RSE is part of a whole school health promotion project. Emphasis is put on personal and social development of students, cross-curricular dimensions, school ethos, school climate and partnership with families and community. However, RSE has become the preserve of female teachers with fewer male teachers attending in-service. This research explored the attitudes, beliefs and needs of male post-primary teachers with regard to RSE in their school. A qualitative design was employed utilizing focus groups. A total of 25 male post-primary teachers took part in five focus groups. Two of the groups consisted of men who had participated in RSE training; the other three groups were with men who had not. The analysis of the data suggested that there was reluctance on the part of male teachers to teach RSE, and that they feel under threat about their personal and professional identity. They felt under threat both from internal personal forces, in the form of mental models assimilated through personal history and upbringing, and from external organisational forces, communicated through the local school and wider social culture. The data indicate the need for professional development and support that is tailored specifically for male teachers. In order to support male teachers to become more involved in school health promotion and in the teaching of health curricula, pre-service education needs to prioritize key issues such as gender roles and identity.