Transdiagnostic treatment is a new approach in clinical psychology, in which rumination and perfectionism have been proposed as transdiagnostic factors involved in development and maintenance of emotional disorders. The present study aims to analyze whether the presence of general and specific symptoms of anxiety and depression, assessed by the Spanish version of the Revised Children’s Anxiety and Depression Scale (RCADS), are related to rumination (reflection and negative rumination) and perfectionism (self-oriented and socially oriented perfectionism), assessed by the Spanish versions of the Ruminative Responses Scale (RRS) and Child and Adolescent Perfectionism Scale (CAPS). The sample consisted of 314 adolescents (145 boys and 169 girls) aged between 12 and 17 years. The results confirmed that both perfectionism and rumination were associated with general anxiety and depression symptoms, and with specific symptoms of each disorder. The findings have implications for implementation of transdiagnostic cognitive-behavioral therapy-based preventive interventions for anxiety and depression among youths.