Children of parents with mental health problems represent a high-risk group for developing mental health problems themselves. Beside genetic factors, environmental factors - such as socioeconomic status, family characteristics, and stressful life events - are involved in the transmission of mental health problems from one generation to the next. Family functioning is a complex, multidimensional construct encompassing several conceptual domains. In families with parental mental health problems, family functioning is clearly impaired in contrast to the total population. Family functioning is an important factor for the course of parental mental problems but also particularly for the mental development of the children, with an impaired family functioning predicting impaired mental development of the children. Therefore, family functioning has become a focus of family interventions that are aimed at reducing transgenerational dissemination of mental health problems. Beardslee and colleagues developed a cognitive behavioral prevention program for families with depressive parents that showed, among others, a lower incidence for depressive symptoms in children after a 6-year follow-up compared with the control group. At the same time, there is a lack of experimentally controlled intervention programs for children of mentally ill parents in German-speaking countries. The aim of the present study was to evaluate the effectiveness of the family-oriented intervention program CHIMPs (children of mentally ill parents) with regard to changes in the criterion of family functioning. The CHIMPs intervention is based on the model of psychosocial mediation by Mattejat and colleagues, the work of Beardslee and colleagues, and an assessment of need results. Family functioning was assessed via the indications of all family members (mentally ill parent, partner, child) on the Allgemeinen Familienbogen (FB-A) as well as the indications of the therapist on the GARF scale. The sample consisted of 19 families in the intervention group and 14 families in the control group. Data from three measurement points (before the intervention, after the intervention, and 1 year after completion of the intervention) where analyzed. Compared with the control group, mentally ill parents who took part in the intervention group improved in the scale of Task Fulfilment and the relationship scales Emotionality and Affective Family Relationships of the FB-A. Therapists' indications about family functioning suggested improvement; however, this effect is countered by a change in the opposite direction of the control group, impeding a significant intervention effect. Over all three measurement points ( pre-post, 1 year follow-up) the total scores of the scales Communication, Task Fulfilment, and Values and Norms within the family improved. However, the improvement was restricted to the indications of mentally ill parents only. Changes in family functioning as indicated by the partner and children were not significant. The results show evidence of an improvement in family functioning from the mentally ill parent's perspective after the CHIMPs intervention.