Certain pediatric liver transplant patients with immunosuppression levels in the therapeutic range and normal liver function tests present histological alterations (inflammation or fibrosis) in protocol biopsies. The objective of the study was to evaluate the histological findings of protocol biopsies performed at 2, 5, 10 and 15 years after liver transplantation in pediatric patients. A follow-up biopsy is also performed 1 and 3 years after liver rejection. To do that, a cohort study will be carried out by collecting clinical, analytical and histological data of patients undergoing post-liver transplant follow-up in pediatric hepatology and liver transplant outpatient clinics. According to the follow-up protocol for these patients, a liver biopsy is performed at 2, 5, 10 and 15 years after the transplant. In addition, ultrasound, elastography and general analysis with autoimmunity and HLA studies are carried out. The evaluation of the histological evolution of the liver graft and its relationship with clinical and analytical changes will favor the management of immunosuppressive treatment in pediatric patients with liver transplants.