Background To support the process of effective family decision making, it is important to recognize and understand informal roles that various family members may play in the end-of-life decision-making process. Objective To describe some informal roles consistently enacted by family members involved in the process of end-of-life decision making in intensive care units. Methods Ethnographic study. Data were collected via participant observation with field notes and semistructured interviews on 4 intensive care units in an academic health center in the mid-Atlantic United States from 2001 to 2004. The units studied were a medical, a surgical, a burn and trauma, and a cardiovascular intensive care unit. Participants Health care clinicians, patients, and family members. Results Informal roles for family members consistently observed were primary caregiver, primary decision maker, family spokesperson, out-of-towner, patient’s wishes expert, protector, vulnerable member, and health care expert. The identified informal roles were part of families’ decision-making processes, and each role was part of a potentially complicated family dynamic for end-of-life decision making within the family system and between the family and health care domains. Conclusions These informal roles reflect the diverse responses to demands for family decision making in what is usually a novel and stressful situation. Identification and description of these informal roles of family members can help clinicians recognize and understand the functions of these roles in families’ decision making at the end of life and guide development of strategies to support and facilitate increased effectiveness of family discussions and decision-making processes.