Prior research has identified the offline thoughts, feelings, and behaviors that lead to impaired relationships for individuals high in social anxiety (HSA; e.g., fear of conversation; interpersonal aloofness). We tested whether social anxiety manifests through visible online signals of relationship impairment that mirror these known offline indicators, and whether observers use these signals when judging social anxiety online. Facebook profile owners (n = 77) reported social anxiety, their profiles were coded for objective features, and unacquainted observers (n = 6) rated profile owners' social anxiety after viewing their profiles. HSA individuals' Facebook profiles were shown to contain signs indicating relationship impairment across the domains of social inactivity (e.g., few friends and photographs), close relationship quality (e.g., relationship status of single), and self-disclosure (e.g., absence of status updates), and observers inferred high levels of social anxiety in individuals' whose profiles showed these signs. These findings suggest that offline relationship impairment experienced by HSA individuals carries over into online contexts, and that online relationship impairment can be accurately perceived by unacquainted observers. Discussion considers whether integrating this knowledge into existing treatments - most notably online, self-guided protocols - could improve the identification and treatment of social anxiety. (C) 2015 Elsevier Ltd. All rights reserved.