In order to cope with the diagnosis of mental illness in a family member, siblings may be forced to adjust their roles in the family. Taking into account the crucial role that some siblings play in caregiving for the mentally ill especially when the parents are no longer available, it is imperative to develop awareness of their unique needs and address them. Thirty-three adult siblings of people diagnosed with a mental disorder completed the Role Behaviour Inventory (RBI) and a general questionnaire including open-ended questions regarding the roles they played in their families of origin. Findings from the inventory and general questionnaire suggest that the well siblings score higher on two roles, the Hero and Lost Child, and lower on the Mascot and Scapegoat roles relative to a comparison group (N = 33). Being a sibling caregiver emerged as a risk factor to assume certain dysfunctional roles in the family. Implications for future research and therapy are discussed.