Sectorisation is the establishment of small geographical catchment areas with dedicated mental health staff providing services to all patients living in the area. This model of care became very widespread during the 1980s in England and Wales: 81% of District Health Authorities responding to a postal questionnaire in this study were sectorised, and around three-quarters of these had become sectorised after 1980. However, this has occurred without central planning and with very little evaluation. Important questions remain to be answered about its efficacy for the severely mentally ill, about the provision of 24-h cover in a sectorised service, and about which services are appropriately provided at a sectorised and which at a centralised level.