The Unified Protocol for Transdiagnostic Treatment of Emotional Disorders in Adolescents (UP-A) is a well-established transdiagnostic cognitive-behavioral therapy (T-CBT) intervention. The aim of the present study was to examine the efficacy of the program Learn to Manage your Emotions [Aprende a Manejar tus Emociones] (AMtE), a self-applied transdiagnostic internet-delivered program based on the Spanish version of the UP-A. This is the first transdiagnostic internet-based program designed for the treatment of emotional disorders in adolescents.