Objective: Hematopoietic stem cell transplantation (HSCT) can compromise longterm health and social functioning. We examined the impact of physical and socialemotional factors on the social functioning of long-term adolescent and young adult (AYA) HSCT survivors. Methods: This cross-sectional analysis included HSCT recipients from the INSPIRE trial [NCT00799461] who received their first transplant between ages 15-39. Patient-reported outcome measures included the Short Form-36v2, Fatigue Symptom Inventory, Cancer and Treatment Distress, and the ENRICHD Social Support Inventory. We used hierarchical multiple linear regression to identify physical and social-emotional factors associated with social functioning at the baseline assessment, with the first block including sociodemographic and clinical factors significant at P = <0.10 in univariate testing, the second block including fatigue and physical function, and the third block including social support and distress. Results: Participants (N = 279) were 52% male and 93.5% white, non-Hispanic, with a mean age of 30.3 (SD 6.6) at first transplant. Social Functioning mean was 48.5 (SD 10.5), below age-adjusted norms (t = −13.6, P = <0.001). In the first block, current chronic graft-vs-host disease accounted for 5.5% of the variance (P = <0.001). Adding fatigue and physical function explained an additional 46.6% of the variance (P = <0.001). Adding distress and social support explained an additional 7.7% of the variance (P = <0.001). The final model explained 59.8% of the variance; distress, fatigue, and physical function were significantly associated with social functioning. Conclusions: Distress, fatigue, and physical function are associated with social functioning and interventions targeting these symptoms may help to improve SF among long-term cancer survivors treated with HSCT as AYAs.