In England, the theme of promoting collaborative working between social and primary health care remains high on the policy agenda. The underlying assumption, largely untested, is that a greater degree of structural integration benefits service users. This paper reports the findings from a feasibility study comparing two models of joint working and examining the relative impact of personal characteristics, service use and co-location on the likelihood of older people remaining in the community. Baseline standardised interviews with 79 older people aged 75 + with complex needs in two social services departments were carried out following referral, covering social circumstances, physical and mental health and services received, with follow-up interviews after six months. Contacts between social workers and primary care were tracked. The findings suggest that co-location does not necessarily lead to substantially closer interprofessional working in terms of greater contact between social workers and GPs or social workers and community nurses. Factors affecting outcome were degree of cognitive impairment, intensity of home care received and whether the older person lived alone. Whatever the model of collaborative working, its effects on remaining in the community must be assessed in the wider context of the characteristics and services received by older people.