--- - |2 We investigated the developmental implications of online social interactions among 590 youth transitioning to university. We observed friends' posts on participants' Facebook pages, and considered attributes of friends' posts used to indicate positive and negative relationship quality in face‐to‐face interactions. After statistical control of beginning‐of‐year functioning and participants' Facebook content, Facebook friends' deviant content posts (swearing; illegal/sexualized activities) predicted participants' lower grade point average, Facebook friends' posts indicating connection to participants predicted participants' lower psychopathology, and Facebook friends' verbal aggression posts predicted participants' lower institutional attachment, by the end of the year. Negative effects of friends' posts were strongest for participants who were disliked by peers face to face. The online context may uniquely influence youth adjustment in conjunction with face‐to‐face relationships. - Journal of Research on Adolescence, EarlyView.