Patients who had received radioiodine treatment for hyperthyroidism were followed up by two different methods. 576 patients (group 1) were followed up conventionally by their general practitioners and as hospital outpatients. 609 similarly treated patients (group 2) were followed up by a computer-assisted system, the Scottish Automated Follow-up Register (S.A.F.U.R.). Follow-up in the two groups were compared on the basis of cost-effectiveness. On average, patients were seen for follow-up about once every 8 months if in group 1 and every 14 1/2 months in group 2. The overall cost of follow-up and treatment for group 2 patients was less than 60% of that for group 1 patients. A central follow-up register is reliable and cost-effective, particularly so when patients are dispersed over a wide area.