OBJECTIVES To examine the cost-effectiveness of thermal balloon endometrial ablation (TBEA) and levonorgestrel intrauterine system (LNG-IUS) one year after treatment in a group of patients with idiopathic menorrhagia in a public hospital in Hong Kong. METHODS The subjects were patients who were previously recruited in a randomized clinical trial to compare their health status after treatment with TBEA or LNG-IUS. The study design was a retrospective review of case history of the group of patients who participated in the earlier study. Study endpoint was at one year after treatment with a satisfactory control of bleeding. Cost items collected included medications, laboratory procedures, duration of hospital stays, transfusions, use of emergency room/intensive care unit facilities, outpatient clinic follow-ups, visits to private doctors etc. The unit of measurement was cost per successful treatment. Differences in costs and efficacy rates were analyzed by the appropriate statistical tools. The study was performed from a government's perspective. RESULTS A total of 44 patients were evenly randomised to receive LNG-IUS treatment and TBEA and evaluation was performed 1 year after treatment. Of these, 18 patients from the LNG-IUS group completed the study with 3 dropouts. Ten achieved menorrhagic control and 5 had to be converted to other therapies. In patients receiving TBEA therapy, 7 dropped out and 15 were deemed successful. The overall cost of treatment for LNG-IUS and TBEA groups was HKD140,000 (USD18,000; 1USD= 7.8HKD) and HKD430,000 (USD55,000) respectively. The average cost per successful treatment per patient was therefore HKD14,000 (USD1,800) and HKD28,600 (USD3,660) for the LNG-IUS and TBEA patients respectively. CONCLUSIONS From this small group of patients enrolled in a clinical trial to assess the outcomes of LNG-IUS and TBEA, it appears that the LNG-IUS therapy is more cost-effective. The major cost drivers appear to be the procedural and hospitalization costs arising from TBEA.