The founder of CBASP, James McCullough assumed that the interpersonal problems, which chronically depressed patients often experience, and which can fuel into the severity of the depression, have their roots in childhood maltreatment. These interpersonal problems also impair the relationship between patient and therapist and thereby impede effective psychotherapy. Against this background, CBASP was conceived to include an explicit focus on the therapeutic alliance, which is targeted with specific interventions. The present study examined how CBASP compared to an unspecific supportive Psychotherapy (SP) with regards to the therapeutic alliance. It was studied whether there were differential effects of these two forms of psychotherapy in patients with differing degrees of trauma. The study was part of a larger randomized controlled trial on the efficacy of CBASP versus SP. The results indicate that patients in the CBASP group rated the therapeutic alliance on the average more positively than patients receiving SP, and that these evaluations became more favorable in the course of time in both conditions. The differential effects of the respective treatment group on the increase in favorable ratings for the alliance also differed significantly between CM groups. This was primarily due to patients with high CM receiving CBASP, who correspondingly rated the improvement in the alliance higher than high CM patients receiving SP. It appears that CBASP is more effective than SP in creating a positive therapeutic alliance. Moreover, CBASP has a particularly positive effect on the increase of satisfaction with therapeutic outcome in the subgroup of patients with a history of severe CM.