Social workers have worked with older people with mental ill health in multidisciplinary teams for many years. Research regarding their contribution is nevertheless sparse. This article addresses this gap. Qualitative data from semi-structured staff interviews were drawn from a multiple case study of community mental health teams (CMHTs) for older people, some with and others without social worker members. Interviews included questions about team roles and the impact of the presence or absence of social workers on team functioning. A grounded theory approach was adopted to analyse the data, enabling issues of importance to interviewees to emerge. Non-social work CMHT staff were found to place a high value on social worker team membership due to their specific skills, knowledge and values, and with regard to communication pathways. Social workers and other team members' views were found to differ regarding whether social workers within CMHTs should operate as generalists or specialists. The findings suggest the need for formal structures extending beyond the co-location of multidisciplinary staff; appropriate and sufficient supervision for social work team members; and the development of more workable and direct referral systems between CMHTs and social services adult social work teams.