The care programme approach was introduced in mental health services in the UK in 1991. It was intended to improve the quality of care and prevent patients losing contact with care services and, by implication, to reduce psychiatric admissions. We did a study to find out if the approach worked. 400 patients from a London inner-city area who had been identified as psychiatrically vulnerable and included on a case register of patients with special needs were randomised into two groups of 200 each. One group received close supervision by nominated key-workers (as recommended in the care programme approach of the UK Department of Health), and the other received standard follow-up from psychiatric and social services. Outcome was recorded after eighteen months. Data on 393 patients was available for analysis. Of 197 patients allocated to standard care, 64 (32.5%) were lost to follow-up compared with 40 (20.4%) of 196 patients receiving close supervision (p = < 0.005). However, patients under close supervision had significantly more admissions (30% vs 18%, chi 2 = 7.61, p < 0.01) and spent 68% more days in hospital than the standard group. The findings of greater hospital-bed use, which differ from those of studies with community-based psychiatric teams, suggest that close supervision by a single key worker, as recommended in the care programme approach, will lead to greater success in maintaining contact with vulnerable patients, but is likely to lead to more psychiatric admissions.