Background A diagnosis of serious mental illness can impact on the whole family. Families informally provide significant amounts of care but are disproportionately at risk of carer burden when compared to those supporting people with other long-term conditions. Shared decision making (SDM) is an ethical model of health communication associated with positive health outcomes; however, there has been little research to evaluate how routinely family is invited to participate in SDM, or what this looks like in practice.