Objective: To investigate the effects of adverse and protective childhood experiences on symptom improvement in outpatient psychotherapy. Method: We evaluated n = 648 completed outpatient psychodynamic psychotherapies. First, we estimated the rate of symptom improvement for each patient using a two-stage hierarchical linear model. We then calculated the direct and indirect influences of childhood experiences on the improvement rate using a structural equation model. Personality functioning, according to the Operationalized Psychodynamic Diagnosis system, was examined as being a possible mediating factor. Results: The presence of adverse childhood experiences was directly associated with a slower improvement rate in psychotherapy. Moreover, a higher number of adverse childhood experiences was associated with greater impairments in the ability to communicate as one dimension of personality functioning, which in turn was associated with a slower improvement of symptoms. Protective childhood experiences were associated with fewer impairments in specific dimensions of personality functioning, but had no direct effect on the improvement rate. Conclusions: Adverse childhood experiences can directly influence the course of psychotherapy. In addition, the communication dimension of personality functioning appears to be a central mediator on which adverse and protective childhood experiences act antagonistically and can thus indirectly affect the improvement rate in psychotherapy.