Previous studies found that the insecure attachment of adolescents towards their mother, father, and peers leads to more internalizing problems and maladaptive cognitive processes (for example, low self-esteem). However, the dynamic between the attachment of adolescents, negative and positive automatic thoughts, and internalizing problems of adolescents is not well understood. The present study proposed and tested a theoretical model in which positive and negative automatic thoughts mediate the relationship between the attachment of adolescents towards their parents and peers and the internalizing problems of adolescents. A clinical sample of adolescents (N=105; mean age = 16.60), diagnosed with internalizing disorders, have filled out the evaluations for this study. All analyses were conducted in RStudio, and the mediation models were tested using Partial Least Square Structural Equation Modeling. Our main results are that positive and negative automatic thoughts mediate the relationship between adolescents’ parents- and peer-related attachment and internalizing problems. The biological sex and age of adolescents did not moderate any of the paths in the model. Parents and peer attachment, along with positive and negative automatic thoughts, explained 57 % of the variance in the internalizing problems of adolescents. The main findings of the paper are discussed, and the main caveats are underlined.