Social networking sites feature significantly in the lives of many young people. Where these young people are bilingual, social networking sites may have an important role to play in terms of minority language use and in shaping perceptions of that language. Through a quantitative and qualitative study, this paper investigates the use of language in social networking sites by young Welsh speakers, focussing particularly on Facebook. Language choice and behaviour, factors influencing that behaviour, and attitudes towards use of the Welsh language in Information Technology are explored. The data suggests that there are a number of different factors at play, and that it is necessary to consider language behaviour in social networking sites in the context of offline language behaviour.