Background Post-transplant malignancy (PTM) remains a concern among pediatric kidney transplant (PKT) recipients. Study Design Between 1963 and 2015, 884 pediatric (age 0 to 17 years old) patients received 1,055 PKTs at our institution. Cox proportional hazards models were constructed to identify risk factors for PTM after PKT with time-to-first-PTM as a primary outcome. Secondly, the hazard of death or graft loss was calculated in patients who developed PTM. Results Median patient survival was 33 years (interquartile range [IQR] 18.7 to 47 years); 260 patients died during the study period and 47 had been diagnosed with PTM. There were 235 PTMs that occurred in 136 (15.4%) recipients at a median age of 29 years (IQR 17.8 to 37 years). The percentages of patients with PTM were 13% at 20 years post-PKT and 26% at 30 years post-PKT. Of PTM patients who died, 63.8% died of PTM. Among those who developed PTM, there was a higher hazard of death or graft loss (hazard ratio [HR] 1.62; 95% CI 1.11 to 2.38). In multivariable proportional hazards models, factors associated with PTM were increasing age at PKT (adjusted HR [AHR] 3.14; 95% CI 1.80 to 5.48 for 14 to 17 year-olds compared with children less than 3 years), having a living unrelated donor (LURD; AHR 3.25; 95% CI 1.27 to 8.35 compared with a living related donor), or implanting an Epstein-Barr virus (EBV)-positive allograft in an EBV-negative recipient (AHR 5.66; 95% CI 1.11 to 29.0). Compared with the general population, the cancer rate for PKT recipients was 6 times higher (126 vs 21 per 100,000 person-years). Conclusions Pediatric kidney transplant recipients are at increased risk of PTM, which adversely affects survival. Children receiving transplants at an older age, from a LURD, or who receive an EBV-positive organ, should be monitored closely for the development of PTM.