Purpose Pediatric simultaneous heart-kidney transplantation (sHKTx) remains uncommon in the US and criteria for sHKTx are unclear. We examined outcomes of pediatric sHKTx compared to pediatric heart transplant alone (PHTx). Our objective was to identify a threshold estimated glomerular filtration rate (eGFR) that justified pediatric sHKTx. Methods Data from the Scientific Registry for Transplant Recipients heart and kidney databases were used to identify 9245 PHTx, and 63 pediatric sHKTx between 1992 and 2017 (age ≤21 years). Outcomes included patient survival, acute heart and kidney rejection . Results The median age for pediatric sHKTx was 16 (IQR: 12, 19.5) years, and included 31 males (31/63=49%). Over half of sHKTx (36/63 = 57%) were performed in cases where pre-transplant dialysis was initiated. The risk of death in sHKTx recipients was significantly lower than PHTx alone, amongst patients who required pre-transplant dialysis (sHKTx vs. PHTx: HR 0.4, 95% CI [0.2, 0.9], p=0.01) (Figure 1a). There was no improvement in survival between sHKTx and PHTx in those without pre-transplant dialysis (HR 0.5, 95% CI [0.16, 1.51], p=0.2) (Figure 1b). When stratified by eGFR, PHTx alone recipients had worse survival than sHKTx in the group with eGFR ≤35 ml/min/1.73m2 (n = 37, p=0.04). The 1, 3, and 5 year actuarial survival rates in pediatric sHKTx recipients was 87%, 84%, and 83% respectively, and was similar to isolated PHTx (p=0.5). One-year rates of treated heart (11%) and kidney (7.9%) rejection were similar in sHKTx compared to PHTx alone (p =0.7) and pediatric kidney transplant alone ( p=0.5) respectively. Conclusion Pediatric sHKTx should be considered in heart transplant candidates with kidney failure requiring dialysis, whereas the usefulness of sHKTx in cases of kidney failure not requiring dialysis warrants further study. Pediatric sHKTx may be considered for eGFR ≤35 ml/min/1.73m2.