Individuals living with cancer are faced with numerous treatment decisions that encompass both conventional therapies and complementary and alternative medicine (CAM). Although a beginning body of research has explored the CAM decision-making process by cancer patients, the social context of these treatment decisions has been largely ignored. As a part of a larger grounded theory research project exploring CAM decision-making processes of cancer patients living in British Columbia, Canada, the purpose of this secondary inquiry was to explore how significant others were involved in patients' decisions related to CAM. In total, 61 patients with early and advanced-stage breast and prostate cancer and 31 significant others participated in semi-structured interviews. Using constant comparative analysis, four main types of decisional involvement by significant others were identified: creating a safe place for the patient to make a decision, "becoming a team": collaborative decision-making, moving the patient towards a decision, and making the decision for the patient. Significant others were often found to engage in more than one type of decision involvement as a consequence of several key factors. Within the types of decisional involvement, nine distinct roles in the CAM decision-making process were described by the significant others. The findings of this inquiry extend previous research by highlighting the importance of significant others in cancer patients' CAM decisions and challenge past conceptualizations of autonomy in treatment decision making.