Previous studies have suggested that girls with Turner syndrome (TS) exhibit symptoms of social anxiety during interactions with others. However, few studies have quantified these behaviors during naturalistic face-to-face social encounters. In this study, we coded observational markers of social anxiety in prepubertal girls with TS and age-matched controls during a 10-min social encounter with an unfamiliar examiner. Results showed that girls with TS exhibited significantly higher levels of gaze avoidance compared to controls. Impairments in social gaze were particularly increased in girls with a maternally retained X chromosome (Xm), suggesting a genomic imprinting effect. These data indicate that social gaze avoidance may be a critical behavioral marker for identifying early social dysfunction in young girls with TS.