Background A number of key environmental factors during childhood have been implicated in the aetiology of social anxiety disorder (SAD), including aversive social experiences, traumatic life events and parent–child interaction. However, understanding the nature, interactions and relative contributions of these factors remains unclear. Furthermore, the relation of aversive social experiences to the development of key maintaining factors in SAD requires elucidation. Aims The current study aimed to extend previous research regarding the aetiology of SAD by investigating the relationship between key environmental factors in childhood, negative beliefs and self‐imagery, and the development of SAD. Method Social anxiety disorder individuals (n = 40, 87.5% female, Mage = 20.25 years) completed self‐report measures of social anxiety symptomatology, traumatic experiences and parenting style. In addition, participants were administered interviews assessing various domains of childhood trauma, as well as negative self‐imagery and associated socially traumatic memories. Results Participants reported a high frequency of early traumatic experiences across all domains (physical, emotional, sexual, social and non‐relational), as well as a high degree of parental overcontrol. However, social anxiety symptomatology was most strongly correlated with socially traumatic experiences, and mediation analyses suggest that appraisal of aversive social/peer experiences accounts for the relationship of SAD symptomatology with negative self‐beliefs and imagery. Conclusions These outcomes suggest that social trauma may be a key proximal cause of SAD development, leading to the development of negative beliefs and imagery that subsequently maintain the disorder. These findings have implications for understanding SAD aetiology, and improving treatment outcomes for the disorder. Copyright © 2016 John Wiley & Sons, Ltd. Key Practitioner Messages Negative social experiences have been implicated in the development of social anxiety disorder (SAD), but the role of this predisposing factor remains unclear. Compared with other risk factors for SAD, social anxiety symptomatology was most strongly correlated with socially traumatic experiences. Mediation analyses suggested that appraisal of aversive social experiences accounted for the relationship of SAD symptomatology with negative self-beliefs and imagery. These outcomes suggest that SAD individuals would benefit from interventions targeted at processing socially traumatic memories (e.g., imagery rescripting).