Background. Behavioral dyscontrol and violations of treatment contracts are serious clinical problems during psychotherapy, especially in treating patients with personality disorders. However, little is known about predictors of these treatment-interfering phenomena.Objective. To identify psychodynamic personality characteristics that can interfere with the psychotherapy process as indicated by treatment-disrupting behaviors.Methods. Sociodemographic characteristics, descriptive psychiatric diagnoses, and psychodynamic characteristics were assessed in 89 inpatients with personality disorders in psychotherapeutic treatment. Psychodynamic charac teristics were assessed with the Developmental Profile (DP). DP variables were used to predict impulsive acts, anger outbursts, parasuicidal behaviors, and contract violations. Incremental value was established.Results. In this sample, 4 out of 5 patients engaged in treatment-interfering behaviors during the first 3 months of therapy. In general, treatment-disrupting behaviors were not predicted by baseline DSM-IV Axis I or II disorders. In contrast, impulsive behaviors, anger outbursts, and contract violations were significantly predicted by psychodynamic variables, especially the DP levels Fragmentation and Egocentricity. DP variables accounted for an incremental predictive value of 23% for treatment-disrupting behaviors, over and above demographics and descriptive diagnoses. Parasuicidal gestures were not predicted by either DSM-IV diagnoses or psychodynamic variables. KEY WORDS: personality disorder, psychodynamic diagnosis, Developmental Profile, treatment-disrupting behaviors, predictive validity, incremental value