Background: Evidence regarding the impact of pre-hematopoietic cell transplantation (HCT) marital status on post-HCT outcomes is conflicting. Methods: We identified patients, =40-years within the Center for International Blood and Marrow Transplant Research registry who received a HCT between January 2008 and December 2015. Pre-HCT marital status was declared as either 1) Married/living with a partner, 2) Single/never married, 3) Separated/divorced, and 4) Widowed. We performed multivariable analysis to determine the association of marital stsatus with post-HCT outcomes. Results: We identified 10,226 allogeneic and 5,714 autologous HCT patients with a median follow-up of 37 months (range 1-102) and 40 months (range 1-106) respectively. There was no association between marital status and OS in both allogeneic (p=0.58) and autologous (p=0.17) settings. However, marital status was associated with grade 2-4 acute GVHD (p<0.001) and chronic GVHD (p=0.04). There was an increased risk of grade 2-4 acute GVHD in separated patients compared with married patients [HR 1.13, 95%CI (1.03-1.24)], while single patients had a reduced risk of grade 2-4 acute GVHD [HR 0.87, 95%CI (0.77-0.98)]. The risk of chronic GVHD was lower in widowed patients [HR 0.82, 95%CI (0.67-0.99)] compared with married patients. Conclusions: OS post-HCT is not influenced by marital status, but there are associations between marital status and grade 2-4 acute and chronic GVHD. Future research should consider measuring social support using validated scales, patient and caregiver reports of caregiver commitment, and assess health-related quality of life together with health-care utilization to better appreciate the impact of marital status and social support. [ABSTRACT FROM AUTHOR]