Transgender youth often face difficulties when accessing sexual health services. However, few studies investigate health service providers' perceptions of transgender youth, and fewer focus on sexual health. To fill this gap, our study draws on social representations theory to examine sexual health service providers' perceptions of transgender youth and how this influences the provision of health services for this marginalised population in England. A thematic analysis of 20 semi-structured interviews with service providers, conducted between March and June 2014, resulted in five main themes centred on: binary representations of transgender; transgender as homosexuality; uncertain bodies; unstable mental states; and too young to know. Of the service providers interviewed, many understood transgender within a male/female binary, and perceived being transgender to be synonymous with being gay. There was confusion among service providers regarding transgender youths' sexual organs, and most of those interviewed saw transgender youth as mentally unstable and confused. Finally, many service providers perceived that transgender youth are too young to know that they are transgender and make decisions about their body. Some of these representations were potentially stigmatising and many conflicted with transgender youths' representations of themselves. Training by transgender people is recommended to help address these misunderstandings. [Abstract]