Adherence to a medical regimen has been defined as the extent to which a patient's behavior coincides with clinical prescriptions. In liver transplant patients, adherence to immunosuppressive therapy and to medical indications in general is crucial for short-and long-term outcomes. Nonadherence to immunosuppression carries a risk of graft rejection and potential graft loss, whereas nonadherence to general medical indications (eg, avoiding alcohol intake and smoking after transplantation) may be associated with other complications such as de novo tumors and increasing health care costs. Among adult liver transplant patients, the rate of nonadherence to immunosuppressive drugs ranges from 15% to 40%, whereas the rate of nonadherence to clinical appointments ranges from 3% to 47%. The wide range of reported rates is due to different definitions of the term nonadherence and the variety of methods used to measure adherence in the medical literature. Nonadherence seems to be nearly 4 times higher in pediatric and adolescent patients versus adult transplant recipients. Several nonadherence risk factors, such as high medication costs, psychiatric disorders, the conviction that the medication is harmful, and side effects of immunosuppressive therapy, have been described among adult liver transplant patients. The risk factors for nonadherence in pediatric and adolescent liver transplant patients are psychological distress, the functional status of their families, and the impact of immunosuppressive side effects on their physical appearance. A single approach to promoting adherence to general medical prescriptions has been proved to be ineffectual, so a multidisciplinary strategy should be adopted to achieve significant improvements in this field. The aim of this review is to analyze the published literature on adherence in liver transplant patients with a particular focus on the reported prevalence and the identified risk factors. Patients have been split into 2 age groups (adults and children/adolescents) because the scale of the problem and the potential risk factors differ in the 2 groups.