This study examined whether the promotion of mindfulness in psychotherapists in training can influence the treatment results of their patients. The therapeutic course and treatment results of 196 inpatients, who were treated during a nine week period by nine psychotherapists in training, were compared: in the first phase of the study, the treatment group without (CG, historical control group, n = 55), and in the second phase the treatment group with, (MFG, n = 58) therapists who were currently practicing Zen meditation. The results of treatment were examined (according to the intent-to-treat principle) with the Session Questionnaire for General and Differential Individual Psychotherapy (STEP), the Questionnaire of Changes in Experience and Behaviour (VEV) and the Symptom Checklist (SCL-90-R), and showed significantly better results in the MFG.