Underrepresentation by race and ethnicity in oncology clinical trials, including hematopoietic cell transplantation (HCT), is a known challenge. This analysis studied accrual on Blood and Marrow Transplant Clinical Trials Network (BMT CTN) trials conducted in 2014-20 by race/ethnicity, age, and sex comparing these characteristics with those of potentially eligible patients identified from SEER and CIBMTR databases for the disease, age, and years of interest of BMT CTN studies. Five BMT CTN trials met inclusion criteria, including one autologous and four allogeneic HCT trials. Two studies focused on multiple myeloma (BMT CTN 1302 and 1401), two studies on graft versus host disease (GVHD) treatment (BMT CTN 1301 and 1501), and one study on post-HCT maintenance therapy in FLT3+ acute myelogenous leukemia (BMT CTN 1506). A decline in the proportion of patients from minority racial and ethnic groups was seen from the SEER population to trial enrollees, with the largest drop seen between the SEER population and all patients transplanted (on or off trial) in US transplant centers. Allogeneic HCT trials which allowed alternate donor graft sources had less decrease from the SEER population. No decrease was seen in clinical trial enrollment with respect to older age and female HCT recipients. This study provides insights into the underrepresentation of racial and ethnic minority patients in BMT CTN clinical trials, largely due to lack of access to HCT in general. Pathways expanding access to donors and improving the outreach of HCT programs to underserved populations are needed to improve access to clinical trials.