Background: HSCT remains the only curative treatment for high-risk hematologic malignancies. Reduced intensity conditioning (RIC) has increasingly allowed transplant of elderly patients. However, maximizing outcomes in this population remains a challenge. We examine the influence of BMI and weight changes on HSCT outcomes in the elderly. Methods: This was a retrospective review of 216 patients ≥60 years of age who underwent first HSCT at the Loyola University Medical Center between 8/30/2000-6/15/2017. Pearson Chi-square tests for independence evaluated the associations between categorical variables and timing of recurrence. Fisher’s exact test were used where expected frequencies were <5. Independent two-sample t-tests and ANOVA assessed differences in numerical variables. Results: BMI at time of transplant, defined as underweight (BMI<18), normal weight (BMI 18-25), overweight (BMI 25-30), and morbidly obese (BMI>30), did not impact incidence of cardiac dysfunction, pulmonary complications (Cx’s), renal Cx’s, graft versus host disease (GVHD), paraenteral nutrition (TPN) use, changes in albumin, or mortality. However, there was a trend towards increased disease relapse in those who were not normal weight (p=.08). Normal weight (BMI 18-25) at Day 100 was associated with decreased cardiac dysfunction (p=.02), days of hospitalization (p = .03), and mortality (p = .02) compared to non-normal BMI (BMI < 18 or BMI > 25). But there appeared no difference in rates of renal Cx's, GVHD, TPN use, or relapse. Having >10% weight change at discharge from transplant admission was associated with increased renal Cx’s (p = .007), infectious Cx’s (p = .03), use of TPN (p = .006), length of hospital stay (p = .0002), and mortality (p = .009). However, it was not associated with cardiac dysfunction, pulmonary Cx’s, readmissions by 6 months, GVHD, or relapse. Having >10% weight change at Day 100 was associated with increased risk of acute (p = .01) and chronic GVHD (p = .002) and readmissions by 6 months (p = .01), but not with other Cx’s, relapse, or mortality. Conclusions: Patients who were underweight or overweight at key timepoints may impact complications and HSCT outcomes. Furthermore, maintaining a stable weight during transplant admission and the first 100 days was associated with decreased rates of complications and adverse HSCT outcomes. These findings warrant further evaluation into age-related weight and nutritional targets to improve understanding and optimize HSCT outcomes in this vulnerable population.