The paper describes results from the 'Tracking Project', a new method for examining agency overlap, repeat service use and shared clients/patients amongst social and health care agencies in the community. This is the first project in this country to combine total population databases from a range of social, health care and criminal justice agencies to give a multidisciplinary database for one county (n = 97,162 cases), through standardised anonymisation of agency databases, using SOUNDEX, a software programme. A range of 20 community social and health care agencies were shown to have a large overlap with each other in a two-year period, indicating high proportions of shared patients/clients. Accident and Emergency is used as an example of major overlap: 16.2% (n = 39,992) of persons who attended a community agency had attended Accident and Emergency as compared to 8.2% (n = 775,000) of the total population of the county. Of these, 96% who had attended seven or more different community agencies had also attended Accident and Emergency. Further statistical analysis of Accident and Emergency attendance as a characteristic of community agency populations (n = 39,992) revealed that increasing frequency of attendance at Accident and Emergency was very strongly associated with increasing use of other services. That is, the patients that repeatedly attend Accident and Emergency are much more likely to attend more other agencies, indicating the possibility that they share more problematic or difficult patients. Research questions arising from these data are discussed and future research methods suggested in order to derive predictors from the database and develop screening instruments to identify multiple agency attenders for targeting or multidisciplinary working. It is suggested that Accident and Emergency attendance might serve as an important predictor of multiple agency attendance.