This article comes from a research done by GRITS2 as a result of the award obtained to research projects by the Victor Grifols Lucas Foundation in the year 20094. The research was published in Catalan with the title:"Social Work with families: Social workers" responsibility in the self-determination of vulnerable people" and was meant to know what is the contribution of social workers in processes related to bioethics. The self-determination principle was considered in relation to groups of vulnerable people like children, the elderly and their families. The research analyzed three main concepts: social work and ethics, selfdetermination and vulnerability. Bioethics" laws were also analyzed and related to social work basic principles. The results of the study which was done with the participation of social workers from nine high technology hospitals showed that they were very much involved in decision making processes related to health. They had self-determination as a fundamental principle and they acted as mediators between vulnerable people and their families and with other health professionals.