Poor immunosuppression adherence in pediatric recipients of liver transplant (LT) contributes to late T-cell-mediated rejection (TCMR) in ~90% of cases and increases the risk of mortality. A medication adherence promotion system (MAPS) was found to reduce late rejection in pediatric recipients of kidney transplants. Using quality improvement methodology, we adapted and implemented the MAPS in our LT clinic. Our primary outcome was population-level rates of late TCMR, measured as a monthly incident rate. Three-hundred fourteen patients undergoing LT are currently cared for at our institution. One-hundred sixty-two (52%) are females with a median age of 16 years and a median age at LT of 2 years. Preimplementation, monthly rejection rates were 0.84 rejections per 100 patient-months. After iterative implementation of MAPS over 2.3 years, monthly rejection rates decreased to 0.46 rejections per 100 patient-months, a 45% decrease in late TCMR. Implementation of MAPS was associated with a sustained 45% decrease in TCMR at a single center, suggesting that quality improvement tools may help improve clinical outcomes. MAPS may be an important tool to ensure long-term allograft health. Future studies should rigorously test MAPS across a multicenter sample.