OBJECTIVE--To evaluate the effectiveness and acceptability of centrally organised prompting for coordinating community care of non-insulin dependent diabetic patients. DESIGN--Randomised single centre trial. Patients allocated to prompted care in the community or to continued attendance at hospital diabetic clinic (controls). Median follow up two years. SETTING--Two hospital outpatient clinics, 38 general practices, and 11 optometrists in the catchment area of a district general hospital in Islington. PATIENTS--181 patients attending hospital outpatient clinics. NULL HYPOTHESIS--There is no difference in process of medical care measures and medical outcome between prompted community care and hospital clinic care. RESULTS--14 hospital patients failed to receive a single review in the clinic as compared with three patients in the prompted group (chi 2 = 6.1, df = 1; p = 0.013). Follow up for retinal screening was better in prompted patients than in controls; two prompted patients defaulted as against 12 controls (chi 2 = 6.9, df = 1; p = 0.008). Three measures per patient yearly were more frequent in prompted patients: tests for albuminuria (median 3.0 v 2.3; p = 0.03), plasma glucose estimations (3.1 v 2.5; p = 0.003), and glycated haemoglobin estimations (2.4 v 0.9; p < 0.001). Continuity of care was better in the prompted group (3.2 v 2.2 reviews by each doctor seen; p < 0.001). The study ended with no significant differences between the groups in last recorded random plasma glucose concentration, glycated haemoglobin value, numbers admitted to hospital for a diabetes related reason, and number of deaths. Questionnaires revealed a high level of patient, general practitioner, and optometrist satisfaction. CONCLUSIONS--Six monthly prompting of non-insulin treated diabetic patients for care by inner city general practitioners and by optometrists is effective and acceptable.