The general purpose of the study was to explore the clinical applicability of psychodynamic mother-infant group therapy (PGT) among perinatal drug-abusing women and their infants. The more detailed aims were: First, to develop and describe the psychodynamic oriented group intervention method. Second, to examine the impact of drug abuse on prenatal resources and mental health problems and how they predict postpartum mental health among drug-abusing and non-substance abusing mothers. Third, to investigate the beneficial intervention impacts on substance abuse and program completion and on changes in maternal depressive symptoms and the mother-infant relationship (maternal sensitivity, structuring, intrusiveness and hostility, likewise child’s responsiveness and involvement ).The results were compared between PGT and PSS (psychosocial support) and non-drug abusing comparison groups. Fourth, to demonstrate – with the help of a case study – the factors that may mediate and prevent the intergenerational transmission of trauma and loss in early interaction. The aim was to prevent infant disorganized attachment and to evaluate how the methods derived from attachment theory may demonstrate the effects of an intervention. The study was carried out between 2003 and 2008 and the participants were 101 Finnish mothers and their children. Drug-abusing women participated either in the PGT (N = 26) or PSS (N = 25) interventions at two outpatient family support centers in Finland. The comparison group consisted of 50 non-drug abusing women at a maternity outpatient clinic. The PGT comprised 20-24 weekly three-hour sessions with 3-5 months of follow-up and the PSS comprised individually tailored support lasting on average 12 months and included e.g. home visits, mother-infant support and marital counseling. Assessments were pre-intervention and at 4 and 12 month follow-up. The methods used were background and substance-abuse characteristics, social support, pregnancy related distress, hostility and depression (EPDS, CES-D), coping strategies, and attachment evaluations (AAI, EA and SSP). The results can be summarized as follows: Drug-abusing mothers reported higher levels of pregnancy-related distress, depressiveness and hostility, and lower levels of social support than their comparisons. While facing the demands of pregnancy and painful experiences, these mothers more often used inadequate coping strategies. However, a safe therapeutic context helped them to deal with the stress and to mobilize their perinatal resources. During the intervention and throughout the 12-month postpartum follow-up maternal abstinence and treatment completion were on average 80% in both PGT and PSS intervention groups. Maternal depressive symptoms decreased, although PGT mothers had more depressive symptoms in all assessments. A general improvement was found in the quality of mother-child interaction in both groups. However, maternal hostility decreased significantly only in the PGT group and intrusiveness decreased especially in the PTG group. Attachment-derived methods (AAI, EA, SSP) were helpful for understanding the effects of the intervention and how to prevent the transmission of mother’s unresolved trauma to the infant. The findings highlight that perinatal substance-dependent mothers need programs that offer them safe environments where with their peers they can build a confidential relationship and continuity with a few clinicians. This study may contribute to the research and develop accurately focused intervention alternatives to treat these mothers’ relational traumatic experiences during the rapid transition in order to prevent transgenerational destructive models from being transferred to the offspring.