Purpose: Examine associations of social developmental factors (e.g., peer/parent social attachment, romantic relationships) and perceptions of social acceptance among emerging adult survivors of childhood cancer. Methods: A cross-sectional, within-group design was used. Questionnaires included the Multidimensional Body-Self Relations Questionnaire, Inventory of Parent and Peer Attachment, Adolescent Social Self-Efficacy Scale, Personal Evaluation Inventory, Self-Perception Profile for Adolescents, and demographics. Correlations were utilized to determine associations between general demographic, cancer-specific, and the psychosocial outcome variables. Peer and romantic relationship self-efficacy were assessed as potential mediators of social acceptance in three mediation models. Relationships between perceived physical attractiveness, peer attachment, parental attachment, and social acceptance were assessed. Results: Data were collected from N = 52 adult participants (Mage = 21.38 years, standard deviation = 3.11 years) diagnosed with cancer as a child. The first mediation model demonstrated a significant direct effect of perceived physical attraction on perceived social acceptance and retained significance after adjusting for indirect effects of the mediators. The second model demonstrated a significant direct effect of peer attachment on perceived social acceptance; however, significance was not retained after adjusting for peer self-efficacy, suggesting the relationship is partially mediated by peer relationship self-efficacy. The third model demonstrated a significant direct effect of parent attachment on perceived social acceptance; however, significance was not retained after adjusting for peer self-efficacy, suggesting the relationship is partially mediated by peer self-efficacy. Conclusion: Relationships between social developmental factors (e.g., parental and peer attachment) and perceived social acceptance are likely mediated by peer relationship self-efficacy in emerging adult survivors of childhood cancer.