Background Obesity is an increasing problem in the United States, with one in five adolescents obese. Past studies have shown that pediatric recipients of hematopoietic cell transplants (HCT) may have a higher susceptibility to overweight and obesity. Procedure This is a single-center retrospective analysis of 297 pediatric patients who received HCT between 2005-2018. Patients were divided into four weight categories of underweight (UW), normal weight (NW), overweight (OW), and obese (OB) based on age adjusted body mass index (BMI) conversion scales. Post-transplant outcomes included acute graft vs. host disease (GVHD), chronic graft vs. host disease, viral infection rates, time to platelet and neutrophil engraftment, and overall survival. Results In the pre-transplant period, the percentage of individuals who were UW, NW, OW, and OB were 5.4%, 54.5%, 22.2%, and 17.8% respectively. At the five-year post-transplant mark, those numbers were 10.6%, 48.2%, 16.5%, and 24.7%. Overall, BMI was found to increase 0.00094 ± 0.0001 kg/m2 each day after transplant (p < 0.001), with older individuals demonstrating greater trends of BMI increase. Further, there was a larger BMI increase in those who did not receive TBI compared with those who received TBI (1.29 ± 0.49, p=0.008). The rates of acute graft vs. host disease (GVHD), chronic GVHD, and viral infection, in addition to time to platelet and neutrophil engraftment and 5-year survival estimate, were not significantly different among weight groups. Conclusion Pediatric HCT recipients are at high risk of developing overweight or obesity after transplant.