About 850 adults attend Middlemore Hospital Emergency Department five or more times each year for 'medical' (rather than surgical and other) services. These people might have unmet needs. We will conduct a randomised controlled trial in which half these people continue to receive usual care, and half are assigned to a new care pathway that aims to coordinate their health care and social services. We will use 'process evaluation' to measure whether this pathway is delivered as intended and whether it can be improved. We will compare the two trial arms using patient interviews and record review to compare patient outcomes; and resource data collection to compare costs to the health services and to the patient. Clear answers will interest hospitals in New Zealand and around the world. By involving hospital and primary care professionals in the research team we expect that the research findings will be taken up quickly.